As I understand it, the way to re-establish the tunnel is to do a "cut & cover" operation. There is no way to "go around" the location, it is actually a very short tunnel.
I believe re-establishing the tunnel will actually stabilize the area by eliminating the possibly collapsing tunnel and providing engineered fill around it instead of just dirt dumped in a hole as was done back in the day.
As I recall, the main concern was the vibrations caused by the train running through the tunnel, but as it is now, the train comes pretty close to the tunnel anyways, so it's probably already "vibrating the earth" in the area.
The other tunnel that really needs stabilizing and reopening is the one with the shoe-fly around it; those curves are limiting what can go up the tracks.