With Mondale's death, there are only 12 11 remaining Senators from the 72nd Congress. With the exception of President Biden, all were out of office by 1997. The only other one to even run for office in this century is Mike Gravel in 2008 and 2020. Hopefully they stick around, but there's a chance that by the end of a hypothetical Biden second term he could be the only one.
The 72nd Congress? That Congress met from 1931-1933, in the latter half of Hoover's presidency. Do you mean the 93rd Congress, which met from 1973-1975?