That is a great question, Wes!
Yes, the Mid-Atlantic Ridge is moving at a common rate for continental movement. But remember this movement has been measured at about 2 cm per year. There are no long-term measurements that have been made based on crustal movement. So yes, at the moment the ridge is growing. But will it still be growing 10 years from now? No scientist has any data on any long-term movement, subduction, or uplift. It would be unscientific for us to state that there will be long-term movement. Science must be based on observation and experimentation.
As for your question on what is happening to the other side of the crust. Crustal plates are wet and fairly compressible and have the ability to bend and fit spaces to a certain degree. Remember 2 cm per year is very slow. If this movement continued for even a hundred years that would make for only 6.5 ft of total movement. So really subduction is not necessary for this slow of a movement.
Based on my experience and research in the UM, I have noticed a pattern that cycles are a principle of nature. So I would personally predict that there may be a time in the near future where the Mid-Atlantic ridge will begin to close back together. Then it will reopen and close and repeat. But of course, that’s just my personal prediction. We will have to wait for more long-term data to know for sure!
Let me know if that answered your question!