Ive had people runaway going up and going down. Generally I keep within arms length of whoever im with with so i can grab them in a hurry if anything goes wrong, though if im diving in a threesome it can be difficult.
For a diver dropping down, i just go head down and swim like the blazes till I can grab them and do a buoyant life to the surface.
For those who can not clear their ears easily, this is not an option, as they would be risking considerbale ear injury.
For a diver shooting upwards I do the same, swim upwards as fast as possible, grab them and lift them to the surface.
In this, depending on the depth & rate of ascent, you are risking decompression illness. If that risk is acceptable to you, then do as you must, however it is not a good idea.
This is one of the big reasons why I always dive a wetsuit even in water that's near freezing, I can react very quickly to anything that happens.
If a diver knows how to properly dive a drysuit, it shouldn't be much more different than a wetsuit,... but then I dive my drysuit with considerable squeeze, so ascents & such aren't a major issue.