Take it from a Dad who was trying to find the Holy Grail of Pitching Coaches/programs for my son (among other things), the words Slotty posted are unfortunately accurate.
You can have one of the best PC's that swears to you he is not leaving, only to be gone after you have committed. If your lucky, the Head Coach and or overall program might still be good. However you might be in a situation we were in on several occasions.
For example, the first college we were going to send my son to had a good PC and he (as the recruiting coordinator) was in the process of putting together both an athletic & academic scholarship number. We were only going to get a small athletic number, but had hoped my sons good grades would get enough to where we could afford to send him. Long story short, a lot of time passed during the process, then we didn't hear from the PC for a while. When I called to find out what was going on, the HC said the PC had taken another job. He said he was aware my son was recruited by the PC, but that all the money was now gone for the year. Worse, the academic offer was a decent one, but expired when it languished with the PC before he left. So he would have a spot on the roster, but no money at all. The school was too expensive, so that was that. I would mention the coaches name in this thread, because he is a very good PC, but I am pissed off enough at him not to give him any props.
We eventually decided on another D1 program, but when my son arrived on campus, the PC had left already, and the new PC was from an unheralded D2. We naturally were very disappointed, but what can you do.
Anyway, throughout our Odyssey, we encountered other situations like this, both on our end and also hearing other parents similar stories. My son went to 3 differnt schools, and every one had at least one coach leave. Coaches will come and go, sometimes like vagabonds that hop a train never to be seen again. One great one is going to be in his 3rd program in as many years (details below).
As to the theme of the thread, many good to great PC's have been mentioned. If you get into a program where the HC has a pitching background, plus you have a great PC too boot, you increase the odds of not being left without any quality development so long as at least one stays.
Wes Johnson was with DBU in 2014, and had 6 of the pitchers on his staff get drafted. I wanted to send my son there, but couldn't work out the NCAA transfer credit requirements. Still, Wes left for MSU anyway, so I might be in jail for murder if that had happened to us again. Anyway, he did very well at MSU, having another 6 guys get drafted, with many crediting him for improving their games. However I recently heard he is leaving after one year to be the PC at Arkansas. So if you want your son to get some great teaching in the art of pitching, look into sending him to Arkansas. He will get at least one year with Wes Johnson.