Regardless of whether or not you complete the program, PIs are open to the best possible candidates. The CP is very helpful in terms of being around leaders who can write good recommendation letters. If you are still rehirable, then you can try for the PI, but you had better have a stellar resume. The fact is that any one with a stellar resume in that field is going to beat out a normal CP alum who doesnt have as many skills or experience. So, yes you can still apply and if you have what they are looking for, then you have just as good a chance as anyone.