Good news: This is completely normal. Your other breast will make up the difference, and you will absolutely be able to continue to nurse your baby as long as you would like. When my daughter was about 4 months old, one of my breasts dried up completely. I tried it all and couldn't manage to get any milk to come out, pumping, nursing, etc. I continued to nurse for another 4.5 months and then stopped for unrelated reasons. The working breast just produced more and more milk until it was making as much as two breasts had been.
Bad news: Some other moms may be able to give you advice, but for me, nothing I tried worked. Nothing even helped that much. It was (to the best I can figure) because of the pumping and one breast just didn't pump very well. And I was extremely uneven by the end, with one breast back to pre-nursing size and the other full of two-breasts worth of milk! That was hard on me.
More good news: after I stopped nursing, my breasts evened out again. The one that had been full is not unusually larger now, despite all the stretching it did. You wouldn't even know it, looking at me now.
I hope you have better luck than I did fixing the problem, but even if you don't, your body has ways to compensate, so don't stress too much.