[davelnewton]

If you're not directly profiting from the acquisition, then this is only barely a lateral move, with more work and responsibility (so not really lateral at all).

I would tread carefully: if it's a matter of the heart, that factors in, but: I would attempt to get guarantees from the acquirers before making the move in terms of work/life balance, length of engagement, etc.

It's more likely I'd take them on as a side client, charge per unit of work, but offer documentation and migration work for a (fairly large) fixed fee, and do that while you explore future gigs.

YMMV.