boxing is like music and each round is like a song. every movement sets up another movement until the music stops at the end of each round. it's kind of like jazz where you're improvising as you go, building on the scales and progressions that you know.
combinations are simply scales/patterns that help you learn what goes together. EVERY combination should end with you being in a safe position. If you can still touch your man with either your straight left or right, and definitely a left hook, then chances are he can still touch you.
finishing a combination with your jab is good for beginners b/c your straight right has the right shoulder and your left shoulder "loaded", your finishing left jab is really powerful and will place your body in the closest thing to the ready position off of a punch. but you should still move your feet after, setting up a new position of attack.
finishing with your left hook means that you are for surely in range to still be hit, and your combination should finish with rolling out to the left (if your weight was over to the right leg) or dropping your head to the left (if your weight was on the left leg after throwing the hook).
when you finish with your right, your weight might be more on the front leg which means that you could finish your combination with a step back (first video below) then coming around ...
OR roll out to the right, like a lot of latin fighters are taught (second video below).
if your weight is centered or in your right leg (in a narrow stance) when throwing your straight right you can easily drop your head to the right, taking it off center line and setting up another right (third video) and end with a roll out.
another common lesson for a beginner is to "finish" with your right, return to ready position, and immediately double or triple jab to the left .
any way you look at it, true boxing combinations (not just recreationally hitting the bag) should always finish in a safe position; during the round you are always moving something, hands, head or feet.