Sysdig Monitor uniquely identifies each instance using information other than the host name so reusing host names is not an issue if you assign tags to your instances.
Assign every instance a group tag (either via AWS or the Sysdig agent's tagging capability) and then analyze metrics by the appropriate group. Tags allow you to place machines into logical groups so that, even if machines go up and down, you still get consistent, long lasting metrics for each group.