We’re not planning any feature updates, bug fixes, or support for the deprecated features.
Take a look at this:
We consider that a certain task is deprecated only when the latest
version of that task is marked as deprecated.
When the user searches for deprecated tasks, we push these tasks to
the end and group them under a collapsible section that's collapsed by
default.
If a definition is already using a deprecated task, we would show a
deprecated task badge on the task so that it's clear to the user that
the task is deprecated and hence is not currently being maintained,
there by encouraging them to make a switch to the replacement.
It is recommended to mention in the task description about the new
task that is going to replace the deprecated task.
Source Link: Deprecated Tasks
As for how long before it goes from deprecated to being removed?
Even though some task has been deprecated, but it will be available for a while.
We understand that moving existing definitions over will take some
time for our customers. As such, we have not determined a date for the
removal. We encourage that new definitions be created with new task
and also move existing definitions over as soon as it is possible for
you.
For delete a task, already answered here. Take care of this, if you need to reinstall a Task, the process is non-trivial.