To salvage the pen you will need to extract from another pen, a lever that
is the exact same size and shape as the one you lost. Not only that, the
diameter of the the barrel from the donor must be the same size as the
pen you're trying to save, since the retaining ring that holds the lever in
place must be extracted and installed in the damaged pen. Barring any
nostalgic value, not likely to be be worth the time, effort and money.
Assuming the sac and JBar are in working order, the pen can be filled
by dipping it in ink and pushing a coin (a dime should do the trick) into
the slot in the barrel. The coin will press down on the JBar, compress
the sac, and when removed, the sac will expand and draw ink. Coin fill,
toothpick fill pens were not unusual a hundred years ago when the patent
for a lever was still active.
If you decide to coin fill it, I'd be cautious about carrying the pen. If
something poked into the slot ( a nail-file, small comb, key, etc.) you'll
have cap and a purse full of ink.
Too bad about the the pen, although it remains safely usable if left on a desk.
Best of luck with it.