Running a long-lived service on Mesos has a significant drawback right now in that Mesos build deploys restart your tasks. This could lead to nontrivial outages for services that have a high warm-up time. Basically everything would need a graceful restart mechanism that basically allows a shutdown/restart with a new version of the code.
With this feature intended(e.g., deploys) or unintended slave restarts (e.g., crashes) will not kill the tasks underneath. When the slave restarts it recovers by reconnecting with the old live executors/tasks.