If you are going to have the tiles redone anyway, you should also check all the pipes behind the tiles and have them replaced if necessary. It looks to me as if the bathroom has seen its best years, and accordingly, the pipes are probably not in top condition anymore. What will you do if you have just had the tiles redone and then a pipe bursts? That would not be the first time something like that happens. My plumber had such a case a few weeks ago with a customer; despite advice, the customer did not have the pipes replaced because you also had to access them from the stairwell, which had just been renovated. Fourteen days later, it became an emergency due to a burst water pipe and had to be done again. The only advantage: maybe part of the cost will be covered by insurance. Perhaps the risk also feels higher if someone has already used a jackhammer or something similar on the old tiles, and nothing would have happened if nobody had touched anything. In my opinion, one should consider having everything done at once, and after that, you will have 20-30 years of peace. Then, the issue with the toilet drain pipe is still the smaller problem in that context. And afterward, you will have a nice bathroom up to current technical standards. Unfortunately, such a renovation is not cheap.