You are assuming that she's not already a 'permanent' problem for the Arthrwyd and the local area. You are assuming that she's not off the backfoot, as of now when we gave her (and ourself, mind) a mid-turn of respite after what I would chalk to be a one-for-one trade-off to her favour.Or we could recognize that Urth has been recognized as being on the road to ascension to godhood and if we do not keep him on the back foot, then he will be a permanent problem for us.
At this point, she's already a 'permanent' problem for us. A mid-long term problem that we should deal according to that term. It'd be better to think of her like Nagash from Warhammer Fantasy or Ganondorf from Zelda. You can hammer her down, you can burn all but the remnants of her empire to ash but you cannot expect that to last until you can be absolutely certain that she's (or whichever way the Lich will refer themselves as) well and truly dead. I mean, the first time didn't stick so how can he now, obviously more powered up than before, be certainly perma-killed?
So what does this mean? Actually following the hint from Oshha would be a way.
Explore Lands = Lowlands or Study Metal options. Figure out ways or allies or just information on the Tyrant would be more helpful. After that, consolidate our gains, make use of the extra action, et cetera. Yes, Urth is trying to Ascend, but at that point, the Lich be well and truly within the realms of the Divine....with a Pantheon of five Goddesses gunning for their new godly arse.Other possibilities including going to the lowlands for allies against Urth or seeking new metals to wield against the undead.