Se l’orlo del vestito si rovina di nuovo, tornerò dalla sarta domani.

In Italian, after se meaning if in a real, possible future condition, you normally use the present indicative, not the future:

• Se l’orlo del vestito si rovina di nuovo, tornerò dalla sarta domani.

Literally, English might expect if the hem will get damaged again, but Italian does not usually say that. The normal pattern is:

• se + present
• future in the main clause if needed

So:

• Se piove, resterò a casa. = If it rains, I’ll stay home.
• Se arriva tardi, ce ne andremo. = If he arrives late, we’ll leave.

Using si rovinerà here would sound unnatural in standard Italian.

Here rovinarsi means something like to get damaged, to get ruined, or to wear out / come apart depending on context.

So:

• l’orlo si rovina = the hem gets damaged / comes undone / gets ruined

It is formally a reflexive/pronominal form, but in meaning it often works like become damaged rather than literally ruin itself.

Compare:

• Ho rovinato il vestito. = I ruined the dress.
• Il vestito si è rovinato. = The dress got ruined.

So in your sentence, the focus is on what happens to the hem, not on who damages it.

Because orlo is a singular masculine noun, and its definite article is normally lo:

• lo orlo

But before a vowel, lo becomes l’:

• l’orlo

This is the same pattern as:

• l’uomo from lo uomo
• l’amico from lo amico

So l’orlo simply means the hem.

Orlo means hem: the finished edge at the bottom of a dress, skirt, trousers, etc.

So:

• l’orlo del vestito = the hem of the dress

This is a very specific sewing/clothing word. It is not just any edge or border.

For example:

• La sarta ha sistemato l’orlo. = The seamstress fixed the hem.

Italian often expresses this kind of relationship with di + article:

• l’orlo del vestito = the hem of the dress

Here del is di + il.

This structure is extremely common in Italian:

• la porta della casa = the door of the house / the house door
• il colore del muro = the color of the wall

English often prefers noun-noun combinations like dress hem, but Italian usually does noun + di + noun.

Because tornare da qualcuno means to return to someone / to go back to someone, especially a person, professional, or someone’s place.

So:

• tornerò dalla sarta = I’ll go back to the seamstress / I’ll return to the seamstress

Da is commonly used with people and professionals:

• vado dal medico = I’m going to the doctor
• torno dal dentista = I’m going back to the dentist
• passo da Maria = I’ll stop by Maria’s place / I’ll stop by to see Maria

Using alla sarta would sound less natural here, because you are talking about going to a person in her role as a professional.

Both could work, but they are not exactly the same.

• tornerò = I will return / go back
• andrò = I will go

Tornerò implies that this is not the first time: the speaker has already been to the seamstress before and expects to go back again.

That fits the sentence well, because if the hem gets damaged again, the speaker will return to the seamstress.

If you said:

• andrò dalla sarta domani

it would simply mean I’ll go to the seamstress tomorrow, without emphasizing the idea of going back.

Di nuovo means again or anew.

In this sentence:

• si rovina di nuovo = gets damaged again

Very often, di nuovo and ancora can both mean again:

• È successo di nuovo.
• È successo ancora.
• both = It happened again.

But ancora can also mean still:

• Sono ancora qui. = I’m still here.

Because ancora has two meanings, di nuovo can sometimes be clearer when you specifically mean again.

Because the sentence has two parts with different jobs:

1. Se l’orlo del vestito si rovina di nuovo
   = the condition (if the hem gets damaged again)

2. tornerò dalla sarta domani
   = the result (I’ll go back to the seamstress tomorrow)

In Italian, a likely future condition usually uses the present in the se clause, while the result can use the future:

• Se ho tempo, ti chiamerò.
• Se viene, parleremo con lui.

So the sentence is perfectly normal:

• present in the if clause
• future in the main clause

Yes. Domani is flexible.

The original sentence is:

• Se l’orlo del vestito si rovina di nuovo, tornerò dalla sarta domani.

That is natural and clear. But you could also say:

• Domani tornerò dalla sarta, se l’orlo del vestito si rovina di nuovo.
• Se l’orlo del vestito si rovina di nuovo, domani tornerò dalla sarta.

The meaning stays basically the same. The position of domani changes the rhythm or emphasis a little, but all of these are understandable.

Yes, abito could also be possible in many contexts, but there is a nuance.

• vestito often means dress or garment/clothing item
• abito can mean dress too, but also suit depending on context

So:

• l’orlo del vestito clearly suggests the hem of a dress or garment
• l’orlo dell’abito is also possible, but it may sound a bit more formal or context-dependent

In a sentence about a seamstress fixing a hem, vestito sounds very natural.

Yes, most likely.

• l’orlo del vestito = the hem of the dress
• la sarta in dalla sarta = the seamstress

The definite articles suggest that the speaker and listener either already know which dress and which seamstress are being talked about, or that the context makes them identifiable.

This is very common in Italian. Definite articles are used often where English might also use them, but sometimes Italian uses them even more naturally than English does.