It happened to me a few times that one of my equipped swords got lost and my first reaction was that they had dissapeared but they had just "moved" by themselves to my inventory so I just re-equipped them.

I assume that you have already looked in your inventory but I just mention it in any case.

One of your swords gets knocked away onto the ground when you fight Letho in the elven baths. If you don't pick it up, you lose it.

Another of your swords gets unequipped and put into your inventory after the whole Shilard debacle (which, since you were about to return to Vergen I'm assuming you went through).

So yeah, if you weren't really paying attention to those two things, I can see how you suddenly find yourself without any swords equipped whatsoever. There's no forced unequip ala Loredo's house so that's the only scenario I can think of.

Aye, sometimes your sword(s) is unequipped, and you can then find it in your inventory. Check there. :)

That was really dumb. I thought I had checked my inventory, but, apparently, I hadn't. I've got them equipped again. Sorry to waste your time, and thanks to everyone for the help.

No worries, everybody loses sight of the swords at one time or another after some in game event unequippes them ;)

Yep, no problem. With the way the inventory works in vanilla (Panel Tweaks to the rescue!), it's not unheard of that you simply cannot locate what you're looking for.