How will I know if this ground is no longer connected?

I had my battery disconnected to replace a starter and
decided to clean some of the various grounds. The
one on the transmission probably hadn't been done
since switching out trannies about 80K miles ago.
When I put a wrench on the connection to the
trans, the bolt broke. (This had perhaps never
been touched in the life of that trans, 23 years
now and 160K on it's first van and 80K more on mine.)
Just what I didn't want at the end of an overly long
starter project. I did notice just about a thread and
a half left on the broken stud. I tried a thin nut
on it and it is holding - for now. So just curious
how will I know if this falls off?

Any quick thoughts on a second choice to connect
this strap? I guess I'll just buy a bit longer strap
and
go to another nearby bolt.

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