very angsty headcanon: since Adahl is older than Maxwell I think it's highly possible, that he dies before Maxwell (at a very high age and after spending many wonderful years with Maxwell of course). It could happen while Adahl sits in the garden, enjoying the sun. He tells Maxwell, who draws a little, that he's tired and will sleep a little. Later Maxwell tries to wake him because he got some snacks for them but Adahl doesn't wake up anymore. Will Maxwell ever recover from it?
In the back of Maxwell’s mind, he always knew that Adahl would most likely die first if they managed to live to old age. Still, he wouldn’t be prepared for when it actually happened and would be extremely heartbroken when he finds Adahl passed away in his sleep. Maxwell along with their children (because at this point Adahl’s kids are his as well) and grandchildren would give Adahl a Dalish burial somewhere near where Maxwell lives so he can visit him every day. I imagine Maxwell would have a bench that he sits on underneath Adahl’s tree and will spend time there drawing or planting flowers and telling Adahl about his day and how their children and grandchildren are doing. Maxwell never ends up falling in love again with anyone else, but he becomes happy again with time. He knows that someday he will be together with Adahl again and takes solace in the fact that Adahl passed away happily and peacefully in his sleep. One day in the future their kids will find Maxwell has passed away during a nap under Adahl’s tree with a serene smile on his face. Maxwell is laid to rest next to Adahl with a tree of his own.