If so, this will probably be depicted as a blow to Obama's presidency. Actually the precedents for presidents switching running-mates after their first term are largely positive; where an incumbent has rejigged the lower half of the ticket and lost, usually the original election had been a bit peculiar. The full list of such elections is as follows:
0) 1800 - Adams / Jefferson: Thomas Jefferson had served four years as John Adams' Vice-President, but because of the problematic electoral system originally written into the constitution he was effectively leader of the opposition. Adams chose a formal running-mate (Charles Pinckney) going into the 1800 election, as did Jefferson (Aaron Burr), and the latter won.
1) 1804 - Jefferson / Burr: a very clear case where Burr was dumped after shooting Alexander Hamilton dead in a duel. Jefferson chose George Clinton as his new running-mate and was re-elected.
2) 1828 - Adams / Calhoun: because of the messy 1824 election, John Quincy Adams, like his father, ended up with a Vice-President who was effectively in opposition to the administration. In 1828 Calhoun ran with the defeated challenger from 1824, Andrew Jackson, and for the second time an incumbent President Adams was defeated by a ticket including his own Vice-President.
3) 1832 - Jackson / Calhoun. Jackson must have regretted teaming up with Calhoun; the relationship went rapidly sour, culminating when Jackson's nominee for ambassador in London failed to get approval in the Senate on Calhoun's casting vote. The unlucky nominee, Martin Van Buren, was chosen to replace Calhoun who thus became the only Veep to be disowned by two successive presidents. Jackson and Van Buren won re-election; Calhoun resigned the Vice-Presidency before his term would have expired.
4) 1864 - Lincoln / Hamlin: with the Civil War at full spate, Abraham Lincoln deemed it better to balance his ticket with a Democrat rather than a fellow Republican, and Hannibal Hamlin was replaced with Andrew Johnson; they won, and Johnson became President on Lincoln's death.
5) 1872 - Grant / Colfax. Schuyler Colfax, elected with Grant in 1868, got involved with a financial scandal, and Grant replaced him with Henry Wilson. Grant and Wilson were elected; Wilson died, quite literally in his office, in 1875.
6) 1892 - Harrison / Morton. Harrison had been elected in 1888 despite having a smaller popular vote than the incumbent Cleveland; Levi P. Morton failed to deliver for Harrison in the Senate, and was dumped for one Whitelaw Reid, who was defeated along with Harrison in the 1892 election. Morton lived to his 96th birthday.
7) 1912 - Taft / Sherman: this is a slightly odd case, in that Vice-President James Sherman, duly re-nominated as the Republican candidate, none the less had to be replaced on election day because he had inconsiderately died the previous week. Taft and his hastily drafted new running-mate Nicholas Murray Butler came third, which is an impressive result for an incumbent ticket in a two-party system.
8 & 9) 1940 & 1944 - Roosevelt / Garner & Wallace. Franklin Roosevelt was elected President four times with three differemt running-mates. John Nance Garner, who served with him for his first two terms, was judged surplus to requirements and relaced with Henry Wallace in 1940; Wallace turned out to be too left-wing and was similarly replaced in the 1944 election by Harry S Truman, who of course succeeded Roosevelt on the latter's death. Garner lived to within a month of his 98th birthday.
10) 1976 - Ford / Rockefeller. Again this is a slightly marginal case: though Gerald Ford was the incumbent president in 1976, he had not even been on the ballot in 1972, but was appointed Veep after Vice-President Spiro Agnew resigned in 1973 and then took the top spot after Nixon's resignation in 1974. His choice for Veep was Nelson Rockefeller, but Rockefeller apparently did not enjoy it and ceded the position of 1976 running-mate to Bob Dole. Ford lost anyway.
So, basically, the portents for re-jigging the ticket are not bad. Jefferson, Jackson, Lincoln, Grant and Roosevelt (twice) changed running-mates and got re-elected. For Adams père et fils, Taft and Ford there are extenuating circumstances which make it an unfair test. The only President who voluntarily rejigged the winning ticket of his first term and then lost his bid for re-election was Benjamin Harrison.
Part of the picture here is that there was no way to replace a Vice-President before 1967. For more than a third of the elections up to 1964, there was no incumbent Veep; seven, including Sherman in 1912, died in office, and eight succeeded to the presidency after a presidential death. (1832 doesn't count here as Calhoun resigned after the election.)
Incidentally we also tried the first episode of the new Veep series last night, but when we realised we had lost count of the jokes about disability in the first ten minutes we turned it off.