What comes next for Iran after strike on Israel?

Small strikes against any IRGC personnel stationed outside Iran - they're fair game and on the table. We're already seeing this with the strikes on Damascus and throughout Lebanon.

Also - based on the saber rattling and talking heads, it sounds like there are likely to be three potential targets: the dams, which would cause massive domestic economic damage to Iran; the oil facilities, which would cause massive economic damage to the Iranian regime; finally, known nuclear sites, which are in line with Israeli rhetoric about preventing Iranian nuclear ambitions.

I think cooler heads will prevail and the dams won't be targeted, and without a regional coalition committed to a ground invasion with a goal of regime change, attacking the nuclear facilities won't have the strategic impact that's desired. Which leaves the oil refineries - there's a natural bottleneck for Iranian oil production/export so there's a short list of physical areas that need to be attacked for it to be effective.

Thinking on it further, IRGC headquarters should also be on the table. I don't think it's likely, but if it succeeds (and it's likely to succeed - especially with direct US support) then it's a huge win. But even if it does succeed I don't see it leading to real regime change in Iran, so without that strategic impact it's far less likely.