You'd Be Rolling The Dice.

"And will replacing the head gasket be enough-- or does the broken/leaky gasket damage the car permanently?" Very possibly permanent damage has developed.

Makes you wonder why they're not fixing it, doesn't it?

CSA

It depends-- usually a blown head gasket in and of itself won't cause any permanent damage, but it can cause overheating and oil contamination which can cause serious damage if the previous owner drove it for a long time that way. It's a tough call for a used car where you don't really know how long it's been like that.

Your mechanic should be able to tell you if the gasket is blown in such a way that it's leaking coolant into the oil-- if it isn't it still might be an okay deal. I would definitely want the sellers to knock at least 400 or 500 bucks of their asking price, though, before it was a good enough deal to be worth the trouble and the risk.

You are taking a chance even if the car was GIVEN to you. Aside from the repairs indicated, there will likely be more, and the engine repair may or may not be enough.

Look up the Blue Book value of this car in average condition and you'll find it is less than $1000, RUNNING!

No. Don't buy this car. With its known problems it's worth just about zero.

The amount of work this car needs at only 100K miles indicates that it has NOT been taken care of. Whoever owns it has just driven and ignored it. Sadly, lots of Corollas suffer this fate because their reputation for reliability makes owners think they never need any maintenance.

Walk away from this and find a better car.