Emily - she's in Canada - different system over there.
GMAA (I'm shortening your name) - I agree that you do need to seek out a 2nd opinion.
I think your Doc has probably written GNRH Analogues (not a specific one of the GNRH drugs but referring to them all in general terms.
They do reduce the bone density and are all contraindicated for ladies with osteopenia, they can only be used for 6 months in a life time in a healthy boned person, so it really doesn't suit your needs on both counts:- the osteopenia and also length of time needed to tied you over to natural menopause.
Visanne (Dienogest) is still in clinical trials and will not be available in the UK for a few years yet - if it passes muster at the end of the trials.
Phase 3 trials just started in China and are due to finish end of 2015 then phase 4 trials begin.
Phase 1 was in Canada which is why you have access to it over there.
Again - it is already known to reduce bone density - but not at the speed that GnRH drugs can do that, so it might be worth considering as a possible option.
If it were me in your shoes I would insist that I have an uptodate DEXA scan on the bone density situation as it is now, before deciding whether to risk further loss or not, and perhaps to have other DEXA scans throughout -every few months - to monitor the situation. You may feel that you can't risk osteoperosis if you have a family history of that then obviously it must be taken in to account.
4 surgeries (1 a big one) may also have bearing on just how much more surgery your tummy can cope with and it could be that the risk of harm from scarring and adhesions will be considered to outweigh the benefits of yet another op.
It is something to consider, and finding the best endo surgeon you can lay your hands on would also mean it is more likely that this next op, if it goes ahead, will be the last in terms of endo. Having a decent job done to remove all existing endo is certainly a goal to aim for.
It certainly isn't a straightforward case because the other medical complications of the osteopenia situation and a previous history of multiple gynae surgery, but I would definitely advise that a 2nd opinion on the surgery side is worth seeking out.
Visanne is still very new product and there isn't a great deal of info yet available.
I am always a bit cautious about why the drug manufacturers do their later clinical trials in so many non-english speaking countries - where patients who report their side effects and experiences online are less likely to be read and understood when written in non-roman script letters. There could be an internet full of unsatisfactory experiences and we won't know unless be happen to also read the languages of the countries involved in the trial.
It seems to have had a mixed response from the overseas ladies who have reported back on this forum, and no one will have yet been on it long term for the length of time you are looking likely to be needing to be on it.
It might be worth a short trial run of 2-3 months to see if it can ease yours symptoms. If that doesn't work and there is no sign of improved quality of life then at least you tried it and you can then leave it and hopefully it won't have done too much extra harm to the bones.
I do think bit more research is needed - and you do need to seek the opinions of other endo surgeons too. Very best of luck.