Can anyone seriously maintain that if a Justice (any Justice) were to pass over the next two years, the GOP wouldn't just force Obama to leave the seat vacant until the next Administration?
could Obama recess-appoint a Justice to SCOTUS?
Yes, but it would not be a lifetime appointment, only until either the Senate rejected the appointee, or until the end of the term. Washington himself used the recess appointment power to appoint a Chief Justice while the Senate was in recess, and the Senate rejected his nominee when they returned. The last president to make recess appointments to the Court was Eisenhower, who did so three times, including for Chief Justice Warren, altho all three of his appointments were confirmed later by the Senate.
However, this assumes the Congress will ever be out of session long enough to permit Obama to make a recess appointment. I really don't see that happening. However, the Democrats could if they wished interfere with the holding of pro forma sessions by making quorum calls and compelling the other members to show up.
How long could a recess apointee last? I remember John Bolton serving as the UN Ambassador for well over a year and never being confirmed.