The four liberal justices are the most likely to leave the court during the next presidential term. Should two of them or one plus Kennedy go, McCain could appoint the most conservative replacements he could find. The Senate could refuse to bring the appointees up for confirmation vote if they wanted, but the remaining four conservative justices would control the court. A four to three decision is just as good as a five to four one. Since there is no constitutional requirement for nine justices, a president could leave a vacancy unfilled if he wanted. There would be no reason for the president to compromise.
That would be a good argument, with one major problem.
It would work, PROVIDED that you have a president with strong, consistent principles who refuses to buckle to the liberals in the Senate. Go ahead and let Chuck Schumer and Co. vote down conservative nominee after conservative nominee. In the meantime, the liberals die off, giving the conservatives majority control. In the meantime, an enraged GOP base takes out its revenge on any 'Rats or RINOs who get in the way.
All in all, a win-win for both conservatives and the GOP!
Think back a couple of years. This is EXACTLY the scenario we faced as Bill Frist prepared to enact the Constitutional Option ending the unconstitutional filibustering of judicial nominations. It would have worked to, except seven RINO senators "reached across the aisle" to stonewall efforts to bring conservatives to the judiciary.
I probably don't have to remind you who led the Gang of 14. It was one John McCain, supported by his girlfriend (and likely VP nominee) Lindsay Graham.
Therefore, your argument is invalid.
The most likely scenario is this: McCain nominates what he calls a "mainstream conservative," most likely a Kennedy/O'Connor type. The 'Rats promptly announce the "right wing extreme" nomination is dead on arrival.
McCain then shrugs his shoulders, says there is nothing he can do and thus, in the interest of comity and bipartisanship, he will reach across the aisle to his good friends Ted Kennedy and Chuck Schumer to determine an acceptable nominee. Said nominee will likely be from David Souter-land.
People who expect McCain to actualy nominate AND fight to confirm conservatives to the SC are purposely ignoring history.