Vis separation by the Tower or 3NM/1000ft. Where I work 15 ILS missed approach turns left to track 015 and the best available departure heading is left to 030. Tower controller is responsible for separation with a missed approach, so where the tracks go into IMC, takeoff clearances will be delayed until sep is assured.
Separation between the missed approach and a following aircraft on final is also easily compromised. In order to keep the 3NM in the event of a missed approach, you need much more than 3NM on final, especially if No.1 is a lightie and No 2 a jet.