If all viruses instantly vanished, would they ever reappear?

Well, viruses are not cells. They are DNA or RNA with protein coats.

@Rarebear Yes, I know that. I was referring the the degeneracy hypothesis, which states that viruses may have come from parasitic bacteria.

If they left yes it is possible for them to return. Perhaps the same way they/all life potentialy came here? Perhaps through meteorite transfer

Things that go away by themselves can come back by themselves.

@PhiNotPi Ah. Got it. The answer to your question, then, is undoubtedly yes.

Viruses can get incorporated into DNA according to this article so DNA might sometimes break down into viruses.