1. There are no more Lumia phones for the near future, the 650 is the last for the year at least. There are some rumors for a top-of-the-line Microsoft smartphone next year that is likely not under the "Lumia" brand.
2. If you buy a Lumia now, you'll have a Lumia now. Official repair services will probably go away maybe a couple years or so after a model is discontinued. But regardless there will likely be parts available for years beyond that and people unaffiliated with Microsoft willing to repair it.
For example Palm is long gone but I still own a Treo 650 and Pre 2. I have some parts lying around (and available online) and can repair them myself if need be, despite Palm no longer existing.