Well, it's not like the transformers are just going to disintegrate. They might blow a winding or crack the core, or on some occasions they'll catch fire, but I suspect in most cases the overvoltage circuits will blow open and shut the circuit down entirely. With no load on the transformer output, the spike might not cause any problems (no load = no current). It might still arc internally if the voltage spike is big enough (similar to what an artificial emp or near lightning strike does to some sites). If that happens then you could just disassemble the transformer, find and repair any problems, and put it back together. Power tools make the work go faster, but they aren't necessary.

Now if the transformer catches fire, then that will go to the recycle bin. I got to see that happen a few times in Baghdad when the grid surged and overvoltaged some of the transformers (one in particular blew up near our office and had us heading for the bunker before we realized it wasn't another stinking mortar barrage. Funny thing, when the surge hit, you could see the power lines up on the poles dancing around some too.