Same here, bought the UM2 4 years ago and it's still plowing through everything I feed it.
I assume you stuck that PEI sheet over the glass?
So you would take out the glass if it was worn down, fairly straightforward replacement I presume.
I like the PEI sheet itself and the quality it gives, but on the MK2 you actually need to disassemble the complete heated bed assembly, put the thing in the freezer for an hour, break off the PEI sheet and then use limonene to peel the glue. All without breaking the heated bed. (like I said: nightmares)
The new magnetic attachment means you just take of the entire plate, exposing the actual heated bed. So they made the PEI a consumable.
There are different ones: You have regular sheet metal with a PEI sheet on both ends, or PEI treated metal in 2 finishes. One is really polished but not very scratch resistant, the other is sturdier. Depends on what you want. Think they even have "regular metal on which you stick whatever you want".
It's pretty cool... If you want to continue printing without cleaning, turn it around.
If you don't want to wait until everything cools down until the print comes lose: buy a second sheet, replace it when the print is done and continue printing. That is something I really like... Waiting for that bed to cool down between prints is a b*ch
If the print doesn't come loose, bend the sheet a bit.
You do have to watch your fingers though, those are some really strong magnets and it pinched my thumb pretty bad the first time because I didn't expect it
I started with a new spool and somehow managed to route the filament so bad on my UM2 that a number of rounds managed to jump over the rim of the spool and that got then pulled together to a point where the feeder could not pull anything anymore - mid way into a 3.5h print. 
