I think they'll be fine.
A lot of people noted that they might have problems with the ranged damage of an arcane but most of evocation is slightly over-rated anyway, a well tooled up cleric will bounce it, a rogue will dodge it and the rest have hit points to soak it.
About the only thing I'd really be careful of is their mobility which is one area that an arcane caster can greatly help out their companions and dispelling magical effects. I guess its not hard to add that ID'ing loot without the arcane or bard running around is gunna be tough too unless theres some scrolls the rogue can UMD.
A few other things to consider if one of them falls over is to get someone to play a dedicated archer, not some cheesy cleric archer, but just a fighter/rogue archer with some levels of Order of the Bow initiate... I made one up the other day and its a bipedal chain-gun, easily doing about the same if not a bit more than an arcane in damage and considerably tougher.
Dunno if that helps but it'll probably give some smartarse something to amuse themselves trolling over.
regards
Threshers dead evoker society.