Further to what @Glenn said above, there's no practical way that a virtualised service like PA can guarantee that persistent tasks won't be restarted. The best that they could manage is some service where they'll automatically restart a process whenever it terminates. You can achieve something like this yourself right now by having a simple scheduled task which does that.
The PA service of automatic restarts has been discussed before, and I think the PA devs acknowledge that it would be useful but they're really busy right now so there's currently no definitive answers as to if or when it'll appear as a feature.