Yes, you can continue to use your existing 110; Obihai isn't going to do anything to disable them.
If you want a spare, you can buy a 110 now, until the end of the year, when they will no longer be sold.
If you don't buy a spare, and your 110 dies, you will be able to use a 200 or 202 with the OBiLINE USB<-->RJ-11 dongle. There were reports of call quality issues with the dongle, but no recent evidence has been added.
See:
http://blog.obihai.com/