If 90210 had continued and both Brenda and Dylan were present: Yes, they would have found their way back to each other and been together.
Being a diehard 90210 and B/D fan I know several things that could justify that claim:
1. Shannen herself on this board called Dylan the love of Brenda's life.
2. Dylan told Brenda that maybe the problem with their relationship (and reason it ended) was that he loved her more than he thought was possible.
3. Kelly told Brenda that one thing that caused her jealousy was that she knew that she would not have Dylan forever and she couldn't help but think that years down the road that Dylan would still remember Brenda as the great love of his life.
4. When Dylan and Kelly were having relationship problems, Brenda told Dylan to try to work through it because if he had come to her after he cheated and everything they had been through and said he wanted her back, she would have taken him back with no questions asked.
5. After a failed engagement, Brenda told Dylan how she couldn't keep any relationship going after losing him because she was still in love with him. When he told her that the right guy would come along, she told him that she had the right guy and let him go (referring to him).
6. Before leaving for London, came to tell him goodbye and that she was still in love with him and knew she would always be.
7. When Dylan got married, he got Brandon to tell her because he didn't think he'd be able to do it. She sent him a telegram telling him that she still loved him and that his future wife had to be quite a woman to get a ring on his finger.
8. When his wife died, he went to Brenda.
9. When he returned to Beverly Hills, he brought Brenda up in conversations when he didn't need to.