By far the easiest way is to try it, but the answer will depend on the channel technology for the incoming leg and that for the attempted outgoing leg, if any, and on why a channel was being allocated. It will also depend on whether the call has been answered by Asterisk and whether there is working early media.
With the gracefully options, calls which are bridged will stay bridged.
I’d expect either the channel unavailable or the congestion one, from either the incoming leg channel driver, or the upstream network, up to and including the phone, in some cases.
(In complex cases the outgoing leg may become an effective incoming leg.)
This will change after the actual stop. Calls are likely to ring out, or give dead air until they time out, depending on whether the upstream needs an explicit “alerting” signal before it starts generating ringback, and whether it always uses early media (e.g. a local analogue phone).