I also hope Nokia Music sticks around for free, but I have a bad feeling microsoft will axe it and push people towards the monthly Xbox music subscription. Or they'll at least put ads in it.
This is really part of a bigger question about what happens to all the Nokia value-added items like Nokia Music, Lumia exclusive apps, Nokia-made apps, etc. It will be hard form Microsoft to produce apps specifically for Lumias if they still want to license the software to other vendors. Nokia really went all out to please their users, because really they had no other choice. They even filled in gaps in basic utilities like trimming videos, ringtone maker, etc. If Microsoft steps up and still produces those apps, exclusives, etc. and makes them available to all Windows Phone 8 devices, that's great. But we've already seen that Microsoft has a limited amount of resources for WP8 and they're currently forgoing working on those features while they push to make the platform work on more hardware. Hopefully the purchase of Nokia means that they'll have those additional resources to work on specific features users are asking for.