I always believe you should give someone a second chance especially family, however if that person has been forgiven many times in the past and continued to go over your boundaries knowing fair well that they were hurting you in the process, then you need to be cautious.
People do genuinly change, especially when they go through some sort of traumatic event, be it, injury, illness or hard times, however there are also people who are very grateful for you helping them out at the time, but once they are on their feet they soon forget what you have done for them and get back to being the person they were when you decided to cut contact with them.
I know I might not have directly answered your question for you, but I hope I have given you food for thought. It is hard when you dont know why the person became estranged in the first place. Good luck and go with your gut instinct.