1x1 RP partners who are worth waiting around for are the ones who are honest and say if they cant post for a while for whatever reason. Most often people are afraid to hurt the other's feelings if they find the rp isn't working out. 90% of the time the other one wants to make it work so will adapt or work with you to make it enjoyable for both of you. If you cant be honest about how you feel about an rp then the other will never know and are unable to fix it. Just because an rp slows down doesn't mean it cant pick back up, or go through a restart. And it doesn't mean you should give up on a partner's writing either. So when prodding, I ask if there is anything I can do to make it easier/better for them or ask how they are doing in case of irl problems. Some people just forget to tell you what's going on, maybe they don't think we even care as 'faceless' people on the internet. But if they really are just blatantly ignoring you, they aren't worth chasing or even wasting time on. 

I always appreciate being told whether someone will be on hiatus or leaving an rp so I can re-open my interest check for new potential writers who are looking for a partner. In the end its just polite to keep communication open. Some people don't realise the amount of time and effort we invest in a story and in that partner, others do. Its just finding the diamonds in the ruff.