Hopeless match, frustration and why Riot should rework Leaver Buster

So this has happened twice now. I wake up, eat breakfast, play with my dog a bit, brush my teeth and I turn on League to play a few rankeds. I get matched with a team where the supp says they can't play supp, so I suggest I'll go supp instead of him and he can take top. Everyone's happy. I enter the game and due to my PC being a little... stupid, it crashes. So I throw my hands in the air, get a little angry and turn my PC back on. Knowing that even if I join the match and win it, I'm still gonna lose LP. So I do my best to do it as quickly as possible, I turn it back on and I join the match about 5 minutes in. Right away I get two assists and our team comes back and eventually wins. Unfortunately I still lose LP. I understand that for leaving games or being AFK you should lose LP but come on, not if it's in the first 5 minutes. It feels like I'm playing the rest of the game for no reason whatsoever, apart from helping out my team get forward in the ranking. Riot please consider reworking this system.

Oh, and does anybody know whether you lose your mmr after such game? Thanks.