4 Di2 systems "here" (cause 1 is at school with kid).
The motors generally don't wear out.
We had 1 1st generation~2010 (?) and the batteries are old now and had to be charged 1/month. The front brifter stopped shifting the FD. That was after a long hard life. The other eTube ones 9000 are doing just great.
I will add the shifting is a little rougher on the cassette than a cable shift. That would mean nothing except we used mostly the Recon alloy cassettes and broke a couple teeth in 2 different cassettes. You would never see this issue on a Shimano cassette.