Blizzard. It's a flat 50SR. Stupid it happens while you queue and DC before even in a game.
It's a bit crazy how much Blizzard has bungled the handling of disconnects and griefing in competitive.
For a player like me who disconnects probably once a month (maybe less), losing 50 SR outright -- for a game that hadn't even started yet! -- makes absolutely no sense. Why not use a graduated system like they do with the temp bans? Yes, you introduce the potential for the system to be exploited but it's a worthy tradeoff. They could even retain a small SR hit (like 10 or 15) to prevent players from preemptively disconnecting from games that they think are lost from the outset.
A second deficiency of their handling of competitive presented itself in my next game, where I was greeted with a player yelling "switch off of Pharah you fucking n-" the instant I joined the game who subsequently switched to Torbjorn (on attack Gibraltar) until I switched off of Pharah. We ended up winning the game but his verbal assault continued until I muted him. What's my recourse for this type of player? To toss out a report into the void? Why doesn't he lose 50SR?