Pete Stark didn't do as well as his previous two elections (both banner Democrat years), but he blew away his competition at 71.6% vs. 28.4%. In fact, the last time he he had an election which he got less of the vote was in 1998, where he scored a measly 71.2%...
Looking back on it, there are only three times in his 38 year history in Congress where he has scored below 60%. His first election in 1972 (52.9% vs. 47.1%), his fourth re-election race in 1980 (55.3% vs. 41.1%), and his ninth re-election race in 1990 (58.4% vs. 41.6%). Even during the Republican wave of 1994 he scored 64.2% of the vote, and this most recent wave saw him at 71.6%.
Honestly, unless the GOP can come up with a moderate candidate *and* politics becomes less polarized (ha!), then I can't imagine a scenario where Stark wouldn't be re-elected.
I'm sure they can change his congressional boundaries, but good luck getting a challenging seat in the East Bay. It's like saying you can redistrict San Francisco or Salt Lake City and see a different result.