We propose a 75% - What you have earned. So if you put in 1 BTC, earned 0.5 since you have been with us. We would happily rebuy our hash power for 0.375 BTC. (Obviously this only applies if your ROI is not up)
Regards,
Katie
Or you could do it the way it was done with hashlets in the beginning. People could place an order to sell-back their miner or just ghs back to you and their order was put on queue where when somebody buys miner/ghs from you - they buy a miner from a sell-back queue and you take a fee for that from the one selling-back.
But exit strategy is not the most important thing you should worry now. Provide proof or everybody will think you are a scam, and rightly so until the proof is given.