Wasn't actually thinking of growing anything on it! Given the methane emissions of livestock, it could just be left to recover. Once ruminants aren't constantly eating it, they'll become more effective carbon sinks. The sheep won't be emitting methane.
You forgot to mention cows, which graze in farmland that could also be rewilded, but which in many cases could actually be converted into arable pastures. I say if needed because of course less farmed animals would free up so many arable fields currently producing livestock feeds.
The idea that we'd have land we wouldn't know what to do with is daft: we need all the carbon sinks we can get, especially given how much of the world is going to become uninhabitable and uncultivable over the next century.
This page breaks down the imbalance and inefficiency of land for grazing within land use:
Half of the world’s habitable land is used for agriculture