What happened to carton and stryver over the years?
Carton died at the guillotine because he switched places with Darnay. Stryver got married to a rich widow and had 3 kids.
I think the question is asking what paths do their lives take, separately and with respect to each other. Stryver is a success, and uses his abilities well. Carton is a failure, though his abilities are greater than Stryver's and he knows it. That is why he works out the strategy for defending Darnay but Stryver is the one who implements it.