Guarda el indicio, no vaya a ser que lo perdamos.

Yes. Guarda is the informal singular affirmative imperative of guardar: guarda = keep / save / put away.

So the speaker is talking to one person in the tú form.

• Guarda el indicio = Keep the clue / Save the clue
• If it were formal singular (usted), it would be guarde el indicio
• If it were plural in Spain (vosotros), it would be guardad el indicio

Indicio means something like indication, sign, clue, piece of evidence. It often sounds a bit more formal or detective-like than pista.

A rough difference:

• indicio = a sign or indication that suggests something
• pista = a clue, often in a more everyday or practical sense

In many contexts they can overlap, but indicio can feel slightly more formal or more connected to evidence.

It is a very common expression meaning something like:

• in case
• for fear that
• lest
• just in case it turns out that

In this sentence:

• Guarda el indicio, no vaya a ser que lo perdamos.

the idea is:

• Keep the clue, in case we lose it
• or more naturally, Keep the clue so we don’t lose it

It expresses a preventive warning or concern about a possible bad outcome.

Not really in the usual sense. In this expression, no is part of the fixed phrase no vaya a ser que.

It does not simply mean not be. Instead, the whole chunk works idiomatically to express concern:

• no vaya a ser que... = in case... / for fear that...

So you should learn it as one expression, not as a normal negative sentence.

Because vaya is the present subjunctive form of ir.

This expression uses the subjunctive:

• no vaya a ser que...

It is a fixed structure, and Spanish uses the subjunctive here because the speaker is referring to a possible, feared, or hypothetical situation.

Even though ir usually means to go, in this expression vaya a ser does not literally mean go to be in a straightforward way. The whole phrase has become an idiomatic way to say it might happen that... or in case....

This is part of the fixed idiom ir a ser inside the expression no vaya a ser que.

Literally, it looks like it might go to be that..., but you should not translate it word for word. The natural meaning is idiomatic:

• no vaya a ser que lo perdamos = in case we lose it / for fear we might lose it

So the best approach is to learn no vaya a ser que as a complete expression.

Because que after no vaya a ser introduces a feared or possible event, and Spanish normally uses the subjunctive for that.

So:

• lo perdamos = we lose it / we might lose it

Here, perdamos is the present subjunctive of perder.

This is not stating a fact; it is talking about something the speaker wants to avoid.

Because the two parts have different subjects:

• Guarda → command to you (one person)
• lo perdamos → we lose it

So the speaker is telling one person to keep the clue because we might lose it.

That can include:

• the speaker + the listener
• the speaker + a group the listener belongs to

Lo is the direct object pronoun referring back to el indicio.

Since indicio is a masculine singular noun, the pronoun is lo.

So:

• el indicio → lo

In English, that would be it.

It could be. Both are possible.

• Guarda el indicio = Keep the clue
• Guárdalo = Keep it / Save it

Using the full noun el indicio makes the sentence clearer, especially if the object has not just been mentioned or if the speaker wants emphasis.

Also remember:

• affirmative commands attach object pronouns: guárdalo
• the written accent is needed to keep the stress correct

Yes, it is very common and natural in Spain. You can hear it in everyday speech when someone is being cautious or warning about a possible problem.

For example:

• Coge paraguas, no vaya a ser que llueva.
  Take an umbrella, in case it rains.
• Haz una copia, no vaya a ser que se borre.
  Make a copy, in case it gets deleted.

It sounds very idiomatic and natural.

Sometimes yes, but it is not always exactly the same in structure or tone.

For example:

• Guarda el indicio por si acaso.
  = Keep the clue just in case.

That is natural, but it is a bit less explicit about what might happen.

The original sentence:

• Guarda el indicio, no vaya a ser que lo perdamos.

spells out the feared result: that we might lose it.

So:

• por si acaso = shorter, broader, more general
• no vaya a ser que... = more explicit about the possible bad outcome

Yes. Some simpler alternatives are:

• Guarda el indicio para que no lo perdamos.
  Keep the clue so that we don’t lose it.
• Guarda el indicio por si lo perdemos.
  Keep the clue in case we lose it.
• Guarda el indicio, no sea que lo perdamos.
  Also possible, slightly more compact

The original version with no vaya a ser que is very idiomatic and common, but not the simplest structure for a learner.