I have heard of exactly one DA*60-250 SDM failure. If you're worried about electric motors failure, there is no other lens you can buy that it is going to be better. All electric motors have failures, sooner or later, so yes you are buying a lens that will eventually fail. Same with Nikon and Canon electric motors. If there is a an electric motor in a lens, it will have a failure rate, that will go up over time. But the Tamron 70-200 is 2.8, bigger and heavier , and is still screw drive. So, if that's your defining issue, get the screw drive. The motor situation was rectified in early 2013, so it's very unlikely even a DA*16-50 or DA* 50-135 would be a problem now. After all, if they can get it to work in the DA* 60-250 and DA*300, both of which have industry standard failure rates, they can get it to work in the DA*16-50 and DA*50-135. But no lens with an internal electric motor can guarantee you there will be no failures. Especially since any bit of resistance, a bit of sand getting into the works, or whatever, that increases the difficulty of focusing is going to stress the motor. That's what is going to fail first, regardless of what the problem is.
So, no, we can't promise you won't experience SDM failure, anymore than Sony or Nikon or anyone else can promise their electric motors won't fail. But anyone telling you to avoid the SDM on a DA*60-250 because of the possibility of failure should know better, unless they are also warning you to avoid the internal electric motors on every other system. Over all, Pentax, according to lens rentals.com has the best frequency of repair in the business. If you're recommending against Pentax because of SDM, you're telling your friend to avoid the best, to buy something worse.
What kind of friend would do that?
If you're that paranoid, be fair, recommend against all internal electric focusing motors. Pentax don't have any particular distinction in that regard, despite what the nervous nellies will tell you.
The advantage to Pentax is, there are still so many screw drive mounts available, if that is something that would make you worry.