Personally, I don't mind losing the MP that much as long as I can continue to play the SP portion of the game. Even with that, there's no guarantee you will be able to play current games at a future date.
For example, I had picked up F1 2010 a couple of months back and decided to install it yesterday. I had a nightmare getting it to run with GFWL and Win XP.
It simply refused to work as GFWL insists it wants to be "patched/updated" before it even allows one to create an "offline" profile. If you cant create a profile, you cant save game progress - period.
Updating/patching GFWL makes it "incompatible" with XP and by extension the game as well because you (apparently) cant run the new GFWL "log in assistant" on XP anymore - it explicitly requires Win 7!
End result? Because GFWL is not "fully/properly" installed under XP, one can run the game but you cant save your progress which is pointless unless you are so pro that you can finish the full game in one sitting. Was finally forced to dual boot into Win 7 and only then could I install and run F1 2010 with "saves" enabled.
What worries me is what will happen once GFWL goes down permanently and there is no way to patch/update it at all? The GFWL client will 'insist" on contacting the online server for a compulsory "update" but will get no reply as it won't exist at that point. You will therefore not be able to create even an offline profile and without that you can't save your game progress.
As for clearing my backlog, that's not really an option for me to be honest. I'm the kind of player who likes to re-play older games from time to time. I am yet to play Fallout 3 (or NV for that matter) though I bought both several years ago. What I do know is, I will want to play them once as the devs intended and then revisit them again a couple of years later with some mods thrown in. Much as I did with HL2 and other titles.
Even if I somehow manage to clear my backlog before the service goes down, what happens if I want to play Fallout 3 again 5 years from now? I simply wont be able to for no fault of mine and despite the fact that I fully meet the "minimum system requirements" for the game and have a legally purchased copy. Pirates on the other hand, will face no such issue. This is what is REALLY annoying. I have paid for a game. I should be able to play it whenever I want provided the "system requirements" are met. Even today I have a fully functional Win9x box for games that explicitly require DOS/Win95/Win98, native 3dfx/Glide support etc. and they all work fine because they don't have any "online DRM" rubbish tethered to them.
With online DRM based DD services, (which is how most PC games are sold today via Steam/Origin/Uplay/GFWL) there are absolutely no guarantees you can play a specific game years from today even if you buy a legal copy and fully comply with the games original system requirements. Read any of the DD services' TOS/SA and you will see why they are so horribly one sided and offer no resolution on this issue.
This is why I dislike these services with their idiotic/intrusive/restrictive DRM not to mention customer unfriendly terms of service. Game devs/pubs are primarily to be blamed for the sorry state of affairs as they opt to use one service or the other sometimes exclusively. Its not like they cant release games DRM free. They can. Gog is a testament to the fact. They just couldn't be bothered to do so.
I fully understand the piracy aspect but I wish there was some sort of rule where devs/pubs would remove DRM restrictions on a game 5-6 years after release. Anyone who genuinely wanted to play it by then will have already done so - legally or not.
The plus would be that even if a game required a specific service/client that was subsequently shut down, customers would still be able to play their legally purchased games...
