1) See this link
https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:5669213349582 for a demo, but of course, that one works because we dont have any transactions in flight (we did a 'shutdown' clean)
In a worst case, if your instance did not cleanly shutdown, then it is possible to still get your database open by setting some underscore parameters,(which you would obtain advice on Support on which ones to set) which would let you get your database open so that you could do a full datapump export to load into a new database.
2) It would probably be noticed on the affected instance first, but it *could* have impacts globally, because another instance may request a read over the interconnect from the affected instance.