As a shop owner and mechanic- I would say that Di2 doesn't wear out any faster than a mechanical derailleur. The shifters actually tend to last longer. Not unheard of to have to replace the battery but there's also been some updates to new batteries that are also the brains of the system allowing for more versatility to be added to an old group just by updating the battery.
Also saw an old comment about not going wireless - as most of you know by now a semi-wireless Di2 Dura Ace group is expected to be announced soon. I have absolutely no inside scoop on that but seems to be the chatter. Wireless levers but wired for the derailleurs.