Can I still use a metal box if the cover plate mounting holes are stripped?
Answer: tap it out one size larger for 8/32 10/32.

Grandfather clause may over rule the following but figured you'd like to know....

First: That box is only rated for 18 21 cubic in. capacity.  You got at least 13 conductors, counting each switch as 2 conductors per Code. 


14 AWG = 13 x 2.00 = 26 Cubic capacity 
12 AWG = 13 x 2.25 = 29.25 Cubic capacity


Plus you're missing a ground jumper which counts as one conductor. (Devices have to be of the self-grounding type to omit bond jumper.)

The switch plate would need to add at least 5 cubic in. for it to work with 14 AWG. Otherwise, you'll need a 1900 box extension to pass muster

Lastly, you maybe wondering about using a larger course screw.  While this is a quick fix certain care should be followed not to allow the sharp threads to damage conductors and not to use a longer than necessary screw. NEC 314.23(B)(1) prohibits using screws and nails