When the game time reaches a certain point, anything above 40-50 minutes, your kda doesn't matter anymore, you can have 2 or 10 deaths and it won't matter, because at that point, both teams have all the core items and most likely full builds, at least carries. So it's really anyone's game at that point, death timers are long and if you just set up one good brush ambush, you can turn the game around. From ~45 minutes onwards, it's anyone's game, so really don't give up, if anything, be glad that you survived for so long, because the chances for you to win are actually higher, since there is no item power difference anymore. Make sure you have vision of a certain area of the map, perhaps their blue buff or just a brush that you know they will walk through, clear it and set up an ambush there with your carries behind you to burst them down as fast as possible. It can work and I've seen it work many times, I know because I was the shot caller for most of those situations. I remember a few cases where we just grouped into that outer base wall brush that is next to the side gate, and they face checked, good game well played. Don't give up.
P.S.: This excludes situations where you have more than 1 inhibitor down and you're just defending the base all the time.