How to say "To lose" as in to "lose a team member"
"输了几个很好的代表？” means a council gambled with their great  representatives,then they lost.

"this year my school's student council lost a couple of great representatives"

今年，我们校学生会失去了几位出色的学生代表。

Most of the time,We can use 失去 for lost。but 失去 indicates some bad conditions. “What happend? politic conflicts or death”。

add an explanation.

今年，由于涉及到毕业，我们校学生会失去了几位出色的学生代表。

今年，由于毕业的关系，我们校学生会失去了几位出色的学生代表。



Edited:
After more consideration,
I think it is better to use either of the two。

失去 means something lost which you wish did not.If you were sorry for the reelection ,you could use 失去。