What do we do if SETI is successful?

Get better camouflage so we don't get get found in the Dark Forrest. https://en.wikipedia.org/wiki/Dark_forest_hypothesis

>The name of the hypothesis derives from Liu Cixin's 2008 novel The Dark Forest, as in a "dark forest" filled with "armed hunter(s) stalking through the trees like ghosts". According to the dark forest hypothesis, since the intentions of any newly contacted civilization can never be known with certainty, then if one is encountered, it is best to make a preemptive strike, in order to avoid the potential extinction of one's own species. The novel provides a detailed investigation of Liu's concerns about alien contact.

That's an allegory for life under authoritarian rule, not a literal alien contact plan

IIRC the author said there are no meta layers of meaning, it’s just honest to god fiction written to be entertaining. I’m struggling a little myself to accept that for the entire trilogy, but that’s that.