Jeep lost 2nd gear

My son’s 1987 Jeep (not a CJ, I think it’s a YJ) just lost 2nd gear. Does this mean he shouldn’t drive it until it’s fixed? Or can he just skip 2nd without harming the tranny? If so, how long could he do that before an expected major failure? And is it cost-effective to have it fixed or should he just install a rebuilt or junk yard replacement?

We just installed an $800 replacement cover (I wish the tranny had failed a month ago!) and he loves his Jeep, so obviously “Sell it now while it still moves” is a last-resort answer.

Assuming there are not large chunks of metal floating around inside, it would be safe to continue driving and skipping 2nd gear. Change the oil and see how it looks.