I am full time employed at a big American bank in London and paid the surgery including all extra costs myself. The Bank had no problem to give me 4 weeks leave, all they asked for is a letter by Betz, which he provided in a matter of a day or two. Right now I am still in my lengthening phase and working full time 5 days a week from home.
I am privately insured via my Bank with AXA, but the policy states something along the lines of "no cosmetic procedures or procedures resulting from cosmetic procedures". Now we all know it is not a "cosmetic" thing as clearly the implications of our condition are much more profound especially if there are leg length discrepancies, but proving that to the insurance company would have been so cumbersome that I didn't want to go down that route because in the end they wouldn't have paid for an intramedullary system from Germany anyway.
As for financing, do absolutely not use loans for this procedure. A loan should be your very last resort if something goes wrong. If you don't have the money to pay for the surgery outright then probably you cannot afford it yet full stop. You don't want to end up in the situation where you have broken legs and money problems.