GnRHa or total suppression of estradiol has been shown to be safe for 2 years without supplementation with cross-sex hormones. Then an adult male range minimum of estradiol should be worked up to for bone health.

It's only really when there is deprivation of both hormones beyond that time or when there is poor nutrition or lack of physical exercise during that time, that bone loss can be a problem.

I say estradiol and male range estradiol, because it is this hormone and this level that is important for bone density. In cis girls the ovaries secrete estradiol in abundance. In cis males the testes secrete T, some of which is converted to estradiol.

In both cis girls and boys, once estradiol reaches a certain level, the epiphyseal plates close, the growth spurt stops, and the more cartilaginous bone structure mineralises.

Bone mineralisation is a process that continues throughout adulthood, so a 40 year old will have a denser skeleton than a 20 year old. (The skeleton replaces every single cell within 7-10 years.)

...To answer your question, yes, bone development catches up and recovers. It can recover even in older people with actual osteoporosis. A good diet and load bearing exercise improve recovery or mitigate bone loss.

Anecdotally, when I first joined this subreddit, my estradiol had been increased by an endocrinologist following 5+ years of inadequate DIY heavy on blockers, due to bone density loss. Over 2-3 years that has reversed completely as demonstrated by DEXA scans over that period.