Depending on your role and class, you can still have an impact if your team refuses to group. As to whether or not that impact will tilt the game to a win is completely up in the air - but at least you have more of a say in the outcome.
You can't force people to do anything in this game, so if they refuse to group - just stop trying to convince them, and stop dying in the effort in trying to do it by yourself. You have no control over your team. Your teammates are either the type of player that will grow a big brain and adjust to the conditions of a losing match, or they are the type of player that keeps headbutting a brick wall, long after their shattered derpy helmet is in pieces on the floor.
At some point you have to bail on team tactics, and let them sort it out themselves. This is completely counter intuitive to a team based game, but this is Solo Q.
I've had games before where I've literally had to split push as a Zilean or Zyra support, because my team was just not grouping for objectives (areas that my champs WANT to play in). But truthfully there isn't any value to dying when the opposing team is going to take an objective regardless if you are there or not.
What you can do, is shove waves and create lane pressure, as safely as you can. Even if you are a support that has half the gold of the lead player in the game, you can still tie up an opposing player by forcing them to catch a crashing wave.
If you as a 5k gold Champion take a 10k gold Champion off the map for a few moments by making them catch waves, you might be able to create a 4v4 for your team, purely based on map position, and without actually telling them to group.
Granted, this is a worst case scenario. Just remember you are going to find yourself in unwinnable solo q games sometimes. It just happens. If you play a solo carry champion, that will happen less, but having a garbage team always going to be a factor in solo q, regardless of what elo you are in. It's kind of a stupid reality of this game that might never change.
