I definitely don't want to see the 358 go as it's a great route. And it seems optimistic it will be saved. But it did have an uncertain future anyway due to bus franchising - where Transport for Greater Manchester will start controlling the local bus network, starting next year and rolling out to Stockport in 2025.
My understanding of the franchising documents is that cross-county boundary services like the 358 would have been exempt from franchising. However under bus franchising Transport for Greater Manchester will buy the large bus depots from the current big bus operators (Stagecoach etc). Companies will then bid to run services from those depots. Stagecoach run the 358 from their Stockport depot, but may not be the company who will operate buses from Stockport depot from 2025. i.e. there could have been a situation where Stagecoach still had the 358 but had no depot to run it from.
Assuming the route's saved, that should also mean its future becomes certain in the franchised world.