The EU would let the UK back in in a heartbeat; the current situation really is good for nobody. It would likely lose the special treatment it had under its previous membership, however.

The EU has repeatedly said we would be welcomed back. Obviously we wouldn't be able to do that unless there was a clear political mandate for that. It would take (in my opinion) at least a generation before those conditions would be possible.

I don't think the UK will try to join anytime soon, but the EU would be silly to not accept them back. The UK is already Europe's second biggest economy, and depending on how Germany goes, could be the biggest in a couple of decade. It has the biggest tech industry in Europe by quite a bit, a relatively healthy demography, a solid military, bases across the world, soft power _galore_).

Like, grudges and personal issues aside, the numbers say the EU would be greatly bolstered with the UK in it.