For anyone that REALLY misses this feature, I would point out that it is possible to set up you own PBX on a Raspberry Pi for around $50 or maybe a bit more (cost of Raspberry Pi 2 + power supply) using the
RasPBX software (pro tip: DON'T install the Incredible PBX addon mentioned on that page; you don't really need it and for most users it's useless bloatware). Then you can loop your incoming Google Voice calls through the PBX as described in
this article, which among other things allows you to use the internal Asterisk voicemail system, which will still provide MWI to your phones.
It's a bit of a convoluted solution just to get one feature back, but it is possible. A far less expensive solution is to simply have Google Voice email you copies of all your voicemails. If you have set up a separate Google account just for Google Voice and you don't normally check the Gmail account associated with that account, then what you can do is log into that Gmail account (NOT Google Voice, you want to be in Gmail but logged in under your Google Voice account) and go to settings and
set up mail forwarding, so that any email that is sent to your Google Voice account gets automatically forwarded to the primary email account that you do check regularly.