Which is the best answer here?

Question

Whether or not we have chosen to use our licenses since then. They remain of enormous value to us.
Which of the following is the best way to write underlined portion of these sentences? If you think the original is the best way. choose option 1.
1. since then. They remain
2. since then, and they remain
3. since then they remain
4. since then; they remain
5. since then, they remain
Please help thanks.
I think is #3 is that correct?

Answer 1

I am far from a grammarian but I would go with #5. However, I'm known as a comma freak; i.e., I'm good at putting in commas to make it sound better. In this case I think it sounds better with a comma AND it is setting off a dependent clause