[Dylan16807]

Oh, you're talking about when it syncs back up. I don't really see the problem.

Next to your offline-capable sine wave generator, put a copy of that cheap safe analog circuit.

Once you get almost in sync, crossfade over to the analog circuit. (If that's even necessary. It might be just fine to swap to it at a zero-crossing.)

Now you're completely in sync. Reconnect to the mains.