Abandons worried dons when students are away (7)
I believe the answer is:
vacates
'abandons' is the definition.
('vacate' can be a synonym of 'abandon')
'worried dons when students are away' is the wordplay.
'worried' becomes 'ate' (something worrying may eat someone up).
'dons' means one lot of letters goes inside another (don means to wear or put on).
'when students are away' becomes 'vacs' (vac is short for vacation).
'ate' placed into 'vacs' is 'VACATES'.
(Other definitions for vacates that I've seen before include "quits" , "Ceases to occupy amid caveats" , "Leaves" .)