That's a different question from whether capacity is available. You could have less than before and still have plenty.
There is also a question of short term vs. long term. In the short term if some things are made only in China they may become temporarily scarce. In the longer term either China will come back online or capacity will be created somewhere else (or both).
This is my opinion, not backed by hard data or numbers or anything else - just my opinion. I think that the world (or at least the west) became dependent on China's capacity. We outsourced and off-shored, and a bunch of factories closed and companies shut down. China didn't add capacity, it replaced capacity. So in the short term, if China shuts down, there's an actual shortage of capacity, because much of the other capacity is gone.
In the long term, as you say, sure, we can start back up here. It will take a while, but we can get there. The buildings didn't die, and the people who knew how to do it didn't all get lobotomies. In the medium to long term, we'll be fine, whether China comes back or not.
Note again: This is my guess. Anyone with real data, feel free to supply it.
There is also a question of short term vs. long term. In the short term if some things are made only in China they may become temporarily scarce. In the longer term either China will come back online or capacity will be created somewhere else (or both).