I definitely think that IF it happens, it's going to have to involve some time travel to get around the issue of players not having played/completed the Crystal Tower storyline yet. In fact I don't think I'd be so fixed on it if there hadn't already been hints dropped that there might be a time-travel plot coming - I'd probably be arguing that he can't possibly be back so soon - but of course if he's from The Future then it hasn't been "so soon" for him!
And while the Crystal Tower is called a "raid" it's really just a big dungeon, certainly at this point when everyone is so overpowered. It doesn't have the higher difficulty that you might associate with the activity of "raiding" being something separate to standard gameplay.
It's also worth noting that anyone who has skipped the Crystal Tower storyline is already missing a segment of an ongoing character's story, as this is where we first meet Nero again after the events of the Praetorium.
I'm also inclined to think we don't defeat as many small enemies as the game shows. If you were adapting this into a non-interactive story form, there'd probably be a lot less killing and a lot more sneaking into places; leaving guards tied up or magically bound rather than dead. Not just marching through the front gates and striking down the entire garrison of probably-conscripted soldiers.