Modern Vespa

So the clip and the pin that holds the rear brake pads in came undone.
So now the brake pads rattle.
Have not been able to put the clip back in and the pin to hold the pads. I realize that I will have to take the wheel off to get to do it right.
Until I do that, besides the rattling, is there any harm to the rear brake pad. I don't use the rear brake 99%of the time, and ride the Vespa till I can fix the problem at hand.

Personally I wouldn't ride it until that was fixed - there is a not inconsiderable risk of the rear wheel locking up, even if the rear brakes are never touched. If you had to do an emergency stop, perhaps you wouldn't stop as effectively as you might.

It sounds like you've lost the tiny spring clip that goes over the end of the pin to prevent it backing out - though the spring at the other end should keep it happily in place. You can use wire temporarily.

You don't need to take the rear wheel off, you can get to these bits with the wheel and the caliper still in place.

I tried to put the clip back in as per your suggestion without taking the wheel off. Unfortunately the brake pad on the drive side of the wheel is not budging and going in for me to slide the pin in. I can get it from the oil filter side but it gets blocked by the brakepad and I dont have a clear shot at using a flat head screw driver and tap the pad in. So for now I haven't ridden it much, just did a short spin and came back.
I couldn't get the 24mm nut off the wheel with a impact driver, need to go get a 1/2 inch breaker bar to fit the 1/2 inch 24mm socket I have. I don't want to put any lubricant in the brake pad area. Weird, murphys law seems to follow me around i.e. simple tasks like this have to become complicated lol. Thanks for the advice.