Accepting organizing duties in a year...but waiting for a new position
It's not so uncommon for a "local" conference organizer to have moved to another institution by the time of the conference, but it's good if there are some actual local conference organizers.  Since you are part of a research group, it seems reasonable that you will not need to be a sole organizer (this wasn't 100% clear from your question).  If you are being asked to be the "primary" organizer, you can still do that remotely, but it also makes sense to ask to instead co-organize it with other people.

So I think the main thing you should consider is: how much do you want to be involved with such a conference, regardless of where you'll be?

Note organizing duties usually count as "professional service" rather than "university service," and organizing conferences can have positive benefits for your career.  If you are doing this as "professional service" rather than as part of your job duties (and it sounds like this is the case since you are getting asked to do it, rather than told to do it), once you make a committment, you should typically follow through.  However, if you do move, then co-organizers are generally pretty understanding that certain aspects are harder for you to do remotely.