He proposed marriage to a girl and she prayed istikhaarah and saw them both and their families in Paradise

Praise be to Allah.

Firstly:

If this girl is religiously committed and of good character, then there is no reason why you should not propose to her again, then complete the marriage contract with her, so long as both of you want to get married. We ask Allaah to make good easy for you wherever it is, and to make it a happy and blessed marriage. 

Secondly:

It is prescribed for the one who wants to get married to pray istikhaarah, asking Allaah for guidance, and to mention by name the girl whom he wants to marry. The girl should also do likewise. If the matter then goes ahead smoothly with no problems, that is a sign that it is good to go ahead and complete the marriage contract, but if he encounters any obstacles that is a sign that Allaah is diverting him from going ahead. 

Istikhaarah does not depend on dreams as some people think. We have discussed istikhaarah and how it is to be done, and commented on the hadeeth about it, in the answer to question no. 11981 and 5882. 

We do not know how to interpret dreams. 

And Allaah knows best.