Currently, Collection symbols cannot be ungrouped. It is possible to modify the collection criteria in order to decide what symbols and attributes to include. But there is no way to revert from a collection and re-use the symbols separately.
The current workaround is to "Modify Collection" -> Copy the content of the collection -> Exit the collection -> Paste the content
It should be natively possible to Ungroup collections as easily as it is to create one.
Revert collection is a feature planned for a future release.
I agree, this would be very helpful.