Koni's can be repaired/overhauled no problem.
Don't have much experience of GAZ, the 2 cars I have been in with GAZ were a joke suspension wise, but others are having better luck, I use AVO coilovers myself as they do so many different versions of coilovers.
I have towed extensively with sierras on coilovers never yet had a problem, but always use a rear brace when doing so, ideally triangulated to the floor as well as between tops.
tabetha