Can a Thief fight a Lawyer

[Clipper]

You would not be able to fight the other monster and then make the deal afterwards. The Lawyers don't say they end the combat, so you can still wander in a new monster after the Lawyers leave, so your second option is OK.

MunchkinMan confirmed that in the post that was linked earlier:

Originally Posted by MunchkinMan

If the Lawyer was the only Monster, then combat is over, unless someone wants to add a new Monster by playing a Monster from their hand with Wandering Monster. Regardless, the Thief will always be allowed to choose to make that "deal" before combat can continue.

If you do make the deal, you get your Treasures before fighting the other monster (one of the very few cases where this occurs), but you can't equip any of them before fighting the monster about to be wandered in.