Tough fight for Lawler for sure, but Robbie has some advantages here.
1. Robbie can make this a brawl. He can close distance and land big shots on fighters who are more technically sound. Thompson, whose fighting style relies on keeping the range, would have to adapt to that.
2. Experiece - Robbie has been around for over a decade and has all that experience. He's been in some very tough fights, especially recently, and even in the parts where he was losing, he was never out of the fight.
3. Toughness - You'd be hard-pressed to find someone who is tougher than Lawler. He can take a beating only to come back and dish it out worse than he got. He's always ready for more. Thompson has to catch him completely unaware and get the KO to finish the fight, which is definitely possible, but would be difficult.
4. Champion experience - Robbie's the champ. That counts for a lot. He's used to the press and the hype and the pressure. Thompson is going to experience it for the first time, so he's at a bit of a disadvantage there.
Very tough fight for Robbie, but he can win.
...and all of this is assuming he beats Woodley and they give Thompson the next shot, which they almost definitely will, but Robbie still has to beat Woodley.