well they can be if you don't keep the battery charged up good but all in all the tips will burn over time, you just have to check them occasionally.
Generally if you start seeing pits in them or material transfering from one side and see it stuck on the other side thats a sign.
They will normally burn just from use so don't be alarmed if you see that, just as long as it's even across the tip surface.

As for a transistor option that does eliminate the contactor issue but you have to deal with the lever switches or sensors that can give problems.
Also the transistor controller is just as expensive as the drive controller, probably about $2500, a reman one probably around $1800, but that all depends on which one it has, prices vary somewhat.
If your using the truck a lot it may be worth the upgrade but if not then i'd just stick with the contact tips, they are a lot cheaper to replace :o) a tip kit is about $100. You may can find them cheaper in aftermarket.
If your use is not heavy and you just put a few hours on it a week chances are you won't have to replace them again for a long while.