No, they do not. I have tested this myself, as I got killed at the very end of the match after the Victory animation came up, and I was kind of upset because I hadn't died all match (gotta keep that perfect KDA). Then I checked my stats, and I had no deaths for the match. So no, killing or dying after the victory/defeat animation starts does not count towards the stats for the match.
Note: As @Schism states, this is true for all stats. For instance, getting hooks as Roadhog after the match end does not increase your hook percentage or count.
According to Jeff Kaplan,
We match based on skill, ping and group size.
So, level shouldn't matter. To further break down what each of those categories are, this post here describes what the matchmaking system looks for when trying to balance teams.
"Skill" in this context refers to two things: your win rate and your MMR. Your win rate is calculated by taking the number of games you've won and dividing that by the total number of games you've played. Your MMR is an invisible number that goes up when you win and down when you lose and is supposed to represent how good you are at the game. Your MMR has to start somewhere, and while your account is new it will fluctuate wildly with each game played as the system is trying to figure out what number best represents your skill based on your average. As you continue to play games, the system becomes more confident in your MMR and the fluctuating decreases. A good matchmaking system will pair up players with similar confident MMR scores, in theory creating even games every time.
"Ping" is a number, measured in milliseconds (0.001 of a second), that
represents how long it takes your console to send information to the
host or server and receive a response back from the server. High ping
is a direct cause of things such as shots not registering, people
teleporting around, getting kills by shooting thin air, and other
issues that people generally associate with lag. Thus, a low-ping
environment is preferable.
"Group size", in theory, should refer to pairing up premade teams of
similar size against each other, mitigating the inherent advantage of
premades (communication, consistent roles, confidence in the skill of
your teammates, etc.) by giving that advantage to both teams. Bigger
premade should = bigger advantage, thus the need for groups of similar
size on each team.
Though, it should be noted, the longer you are searching for matches, the looser the constraints will become in attempt to get you into a game.
Best Answer
Yes and no. Normally, self-damage from explosives and the like does not give the kill to anyone.
RIP-Tire's case is different. It's the same kind of entity as an hero, so kills CAN be attributed to it. This means if you kill Junkrat with the tire, it will count as a kill and it'll even show "Eliminated by [yourname]" along with "[yourname] eliminated".
Fun fact : for some reason, this counts as a shutdown, so there have been some cases of Junkrat players getting PotG by killing only themselves.