If you've got a reason to be gone, then sure. Just post it and we'll note you down. "I wanna play something else for whatever time period" or "I'm going to Canada" or "My hampster died and I must mourn" or "I gave TB up for Lent" or whatever is fine. Just random absence isn't okay. We need to know you didn't just randomly decide to quit TB.
Also, if we see you in-game, that counts. We just need someone to say they saw you and talked to you, or whatever.