With regards to the first question .. it depends.
What do you have in your policy with regards to shortcut creation? If you have "yes in the mailbox" then any ineligible items, and the shortcuts will be moved from the PST to the mailbox and the PST will be deleted (and removed from Outlook). With regards to "no", I am afraid I've not tested to see what that does with the ineligible items. And if you have opted to leave shortcuts in the PST, then the PST will obviously not be deleted, and removed.
Migration failed PSTs should stay as read-only yes. Giving you the chance to correct any problem, and retry the migration.
Hope that helps,
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