If that happens to me while I am in an Arctic Map (not catacomb) that is good. I clear them by whittling down all 9 slugs hit points before killing them off one at a time (NOTE: kill off any that heals first). However, there is also another little trick I do to reduce this from happening. Once a Slug appears, I try to kill it off before it calls for help... BUT, if it does "Call" and this one is still alive, I will attack the newly spawned one and try to kill it off... repeat this if another is called etc until they are all dead. I always kill off Slug / Gigabee in a Wave first.
Oh, and if that happened to me in a catacomb even after all that... I just do the same as some others... town, leave group (since I always make a group before entering a catacomb solo playing), and re-create another one.