I hope you can get some clause added - good luck on that. Not to be a negative nancy, but I bet more than 90% leases don't have such a clause. You pays your monies and you takes your chances. I hear of dozens of stories every year where guys who have leases - sometimes for many, many years - lose them when the property sells. And while it may occur, I personally have NEVER heard of a new buyer honoring a previous lease - even if it is the day before season starts (unless the new owner is part of the same family). It seems that new owners are always eager to hunt the property that they just spent a ton of money on.
You want to be sure not to be kicked off - buy your own piece of dirt.
Not to be rude, but it constantly amazes me the folks that pay a few thousand dollars to hunt a property that is ofter $500K to $1M want all sorts of rights and guarantees over the land owner. All sorts of LO's - from genuine Saints to downright Satans - but when it comes down to it, right or wrong, saint or satan, the land owner is gonna prevail and get or do want he wants - no matter what a piece of paper says.
To me - and this is just me personally - leasing is not about a "contract" - it is an opportunity to build a relationship. You establish a good relationship with the rancher, his land, and his family - and you will be treated fairly, no matter what a paper says. You fail to build a relationship, and when things happen, your paper is no better than TP.