In my opinion and based only on my own experience ,Providing you keep the rock in salt water it should stay alive also I've seen it being kept in polystyrene boxes with plastic bags wrapped around it to keep it damp providing it doesn't dry out it will last easy up to 6 weeks or more,
when adding it back to the tank you may need a bacteria booster to help the rock get back up to pick condition. So don't add any fish straight away and would leave a couple of weeks then start testing to check everything is ok,
Sometimes depending on the condition of the rock you may have to recycle but it will probably be a mini cycle.
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