The Fir Park side are already down due to Jamie Murphy's move to Sheffield United while Ojamaa has been linked with a move to Poland.
Stuart McCall's side are currently striving for a second-placed finish and Hammell believes that particular ambition would be thwarted if there were to be further exits.
"Playing in the European games has been the highlight of my career, without question," said Hammell.
"If we finish second then we know that it opens the door to that again which would be amazing.
"For a club of this size, it is just an incredible experience.
"But we don't want to fall into the trap of looking too far down the line to that.
"There is a lot of hard work in front of us and it is important that we just keep on trying to be as consistent as possible.
"Jamie is a big loss in that respect and I know there has been a bit of talk about Henrik, too.
"If we can hang on to the rest of the squad between now and the end of the current window then it would give us the best possible base to go forward."
The other aspect about finishing in a position that secures European football is the talent that it can then attract – including those who are still at the club.
Hammy said: "If you get to a position where you know you are going to have the chance to play in Europe then it is a real carrot.
"We know that we have quite a lot of our players reaching a point in their contract where they may be thinking about going but having the prospect of playing in Europe can entice them to stay.
"It really is a major thing and there are not too many clubs who can offer you Europe.
"That is why it is so important that we hit the ground running as soon as we get back into things."
Hammell himself is already feeling withdrawal symptoms from football, despite the briefness of the winter break.
The defender indulged himself with a few lazy days on the sofa before his thoughts returned to Fir Park.
"I do really miss it," he smiled. "I've still been watching a lot of football on TV and we had only been off for a couple of days when I started to hanker for it again.
"I'm looking forward to getting back and getting ready for the big push between now and the end of the season."