I'm wondering if I should go to the farewell party for club activities.

　Of course, it's up to you to decide.
As far as I can read the sentences, there is “students who can participate,” and I feel that it is sponsored by the club itself or the teacher in charge.
Since you're probably graduating, and your career paths are probably different, you won't even meet Kinrin Ge anymore, right? And maybe the meeting itself will end in its own way.
What I'm worried about is rather your future. You can probably think “I'm already a department manager or something,” but there are times when you're in a position of responsibility, such as after getting a job. At that time, I would like you to use this thought as a springboard. What kind of person is “recognized as a department manager even if they are not strong”? I think it's a good idea to keep up with this challenge from now on.
This time was summed up as “an experience I just didn't like,” and “I don't participate in the event because I don't like it”... if it becomes a behavioral pattern, it is evaluated as “low aggressiveness” (although that may be fine), and I don't think there is any denying the possibility that communication becomes troublesome when something happens.
In other words, “My opinion is that it's okay to run away, but don't think about getting stronger (stronger) after that.

As a department manager, I think one of your roles is to take over an organization where juniors can continue their club activities happily.
There were probably juniors who were aware of the bullying against you and felt bad about it.
This may be your last chance to end by saying what you want to say as a department manager so that the same thing isn't repeated for the junior generation.
I think it's okay to take this opportunity to run out of steam.

I read it.
I see... while you were working as a club activity manager, you were bullied and harassed and had a very difficult time. And they're worried about whether they should attend the farewell party before graduation. I don't know the details about you or your club activities, but I sincerely understand your worries and painful feelings.
In my personal opinion, I think it's okay not to attend the farewell party until you feel bad about it. It must have been very painful for you to be bullied, bullied, or harassed, and if they don't reflect on the misdeeds committed by the people who bullied them, and if they don't apologize to you in any way, I don't think it's necessary to participate at all if you participate and feel bad again.
It's up to you to make the decision, so I think it's okay to think about it carefully.
Both you and those people will be able to walk your own path from now on. So please throw away the bad things from the past and face your own future firmly.
I sincerely pray that you can live with peace of mind in the future without being bullied or harassed, that you will be blessed with many wonderful encounters and relationships and grow healthily, and that you will live a fulfilling life from the bottom of your heart. And I wholeheartedly support you.

We know that we've had a lot of trouble up until now and have worked so hard. You've got the right skills! How good you are at badminton doesn't determine the manager. I have a lifestyle attitude and attitude of facing each other, so my seniors watched it closely.

What about the other members of the club? They even used acts of violence against you, gimmicks, and bullying. Senpai's eyes were clear. No matter what the other members of the club take, they haven't surpassed you. You should be proud of yourself for serving until the end.

There's no need to get hurt any more. I've finished my duties as a department manager, so I don't need to get involved anymore. Even if you don't participate and talk behind your back, it's just a loser's howling. You should let them bark. That's because I should finish it with my pathetic barking self until the farewell party.

You give yourself praise and praise.
You really did your best.