"Would be cool if the modal is smart enough to display the “Log call & complete task" if call had Connected**,** but offered both “Log call” and “Log call & complete task” option if the call outcome was anything else.”
No. Don’t force the user to complete the task, period. Don’t force them based on parameters, at all.
The fact that these are tied together in this way is a design flaw. This idea is just making a design flaw slightly better, but still adhering to the underlying problem of requiring users to do something they don’t want to without any real benefit or reason.
"Maybe having 2 buttons would work : “log and complete” and “save and skip”
like this ? "
That easy, offer both buttons regards. Problem solved; design flaw solved.