So long as the water can be pumped out faster than it pours in, the underpass can continue to be used.
Except if there is damage or an earthquake or a sinkhole so severe as to cause a major flood, the major concern of keeping it pumped out and open is falling pieces of concrete.
Yes it would take tons of pixie dust to repair.
As far as I know, any hits by oversized trucks to date have resulted in unmeasurable damage to the underpass structure. Either supersized construction methods back ca. 1970 when it was built, and/or magic from the Disney fairies looking after it, has kept the underpass sturdy and standing.
There exist construction techniques that could yield a second underpass next to this one in the event of failure. Such techniques have been used for such tunnels as the Lincoln Tunnel going under the Hudson from New Jersey to Manhattan.