There is no reason why an old bicycle you are comfortable with can't be repaired rather than replaced. Even having a bike that is comfortable to you and you trust is worth quite a bit. If your old bike is gone, you can always hunt for one like it.

As far as the hybrid vs MTB being safer... I'm not sure there would be a huge difference, at least not for a younger rider. The "Faster" might make a difference, as well, if you are riding for longer distances.

However, the other thing you have to cope with is that you are in fact getting older. There are plenty of fit 72 year olds, but strength often decreases, as well as reaction times. So, a slight bump 30 years ago, and you might have recovered without going down, while at 72, it leaves you in a heap on the ground.

Did other aspects of your riding change recently? Retired, allowing more riding? Different riding?