Changed the grip the other day on my mp15 AR15. Picked it up on a whim a bit ago and the safety toggle was loose and almost fell out of the gun? Surely changing the grip did cause this? Something seems to be missing and I'm not quite sure what.

You dropped the spring and/or detent pin when you swapped the grip.

Pull the grip, look on the flat underside of the lower for a small hole. There should be a spring and detent pin in that hole that bears against the round detent notches on the selector. The grip compresses the spring.

The AR has two of these style spring/pin deals. The other is at the rear left and is the detent that holds the rear takedown pin and is held in place by the endpapers.

Same makers thread that hole for a small threaded insert to hold the spring in place.

Found the pin. But now the I need new bolt for the grip and have to retap the hole for said bolt now. Everytime it seems like im losing the stupid springs on this thing when I upgrade...

How many times have you felt the need to change grips?

Why do you have to retap the hole? Did you try to use the wrong size or thread bolt?

Only changed the grip once, didnt realize the pin was there. Changing the retaining pins for the lower has some fun springs. Put a new attachment for a single point sling released another spring. Oh and theres the retaining spring and pin for the buffer tube that likes to get displaced occasionally when you start taking things apart. Thats why they sell Oops! kits.

For the stripped hole, not sure what happened there, put the same bolt back in, thinking the new grip doesnt quite line up right with the hole.

Spring and detent like stated above same thing happens when folks change stocks easy to do.

the detent and spring for the safety are held in place by the grip

you need an oops kit they are about 10-15 dollars to get most of the sprigs and detents to fix those oops moments
https://www.midwayusa.com/product/1019428041?pid=372872