If the only location of your endo is in the bladder then it won't impact your fertility at all from there. Most unlikely it would ever get the chance to escape to anywhere else as there is an escape route - getting flushed out a few time a day.
If you do have endo which is primarily on the outside of the bladder and has invaded from there to the inside then you are at a greater risk of endo spreading from the outside lesion when it sheds and bleeds each month but again there is a pocket there between the bladder and uterus where the endolinings and blood tend to collect.
Having a baby will pause that endo from being active wherever it is located while you are pregnant and should hold out for a bit of breast feeding time afterwards too.
So once you are pregnant then the endo is in a coma and you shouldn't be plagued by it at all through the pregnancy which would be a great help I am sure.
The surgery if you do have it will not improve your fertility at all, it will only preserve the fertility you already have.
If you have raging endo covering the ovaries and the ends of the fallopian tubes then getting that cleared off would improve your fertility chances, but if as you say it is just the bladder then I would be inclined to advise that seeing as surgery will not alter your fertility chances, that you do not have surgery on it, till after a pregnancy.
I had a laparotomy 3 years ago, C-section size hole at the bikini line and my bladder and bowel and uterus were all stuck with endo and adhesions. I do have endo in the bladder and it is still there, but some work was done on the outside.
I had a catheter fitter when i woke up - which was great.
That came out a day or so later.
A few days later I found myself with a full bladder and unable to pee. Urinary Retention is a very common side effect of gynae and bladder surgery. Men and women can be affected.
It is caused by knocking out the the electrical rhythms of the bladder which are supposed to tell the brain when you are full and need to pee and govern the process of actually going to the loo. I then spent the next 17 months on pills to help me to go pee. It was not in the least bit fun, there were plenty of accidents too - not getting to the loo quick enough etc.
These are called Bladder Spasms , you cannot feel them at all, but they are common after surgery down there, and usually sort themselves out after a few days- sometimes a few weeks and sometimes take a lot longer too, as in my case.
Happy to report that one day i did wake up and somehow the electrical signals had corrected themselves into the right sequence again and since then all has been fine. But that was 17months after the op.
I am therefore very reluctant to go through all that again to have the bladder endo seen to.
Bearing in mind the complications that such surgery can give you, even if it is short lived, there is a risk of a longer run of recovery being needed, and it is not something you would want to be battling, while carrying junior around in your belly at the same time.
Ultimately the decision is yours and between you and your surgeon. I can only tell you of my own experience with bladder being messed about with slightly during surgery.
There are some ladies who have had surgery to remove deep endo in the bladder and perhaps they might give you a more positive story of that bladder experience.
In short, if I was in your shoes I'd crack on with baby making asap - leave the bladder till afterwards.