I think I heard somewhere that it's possible to go and talk to the conjurer that teleports you to Icemist to attone for your mistake (I think by paying him a lot of gold) and gain access to Icemist again.
Also another thing I heard someone talk about is, if you already went to Icemist before, to teleport with a teleport scroll to Icemist and when inside, pay up your fine at the Icemist town hall.
I haven't tested them out myself before though, so I can't say for certain they'll work.
I found the relevant thread again.
It seems like your best way is to go is to go talk to the Conjurer near icemist while not attacking any of the Thuramiam knights guarding the place. You'll have to give him the orb of shadows and 10k to make up for your mistake.
Don't do my second suggestion since it seems like that can lock you out of further dialog with the Conjurer if that isn't patched yet.viewtopic.php?f=4&t=16815