Asking the following questions probably helps in designing the right strategies.
1) Is the contract or relation helping supplier de-risk their business model?
2) What would be the supplier response if the contract is cancelled or withhold?
3) Will the contract help supplier to enter a new market or channel?
4) Are the alternative supplier(s) available and are they easily accessible?
5) Can the contract be split or is it required to buy all right now?
6) Is there a merit bundling this contract or order with other orders?
7) Is there a merit and business viability of buyer becoming their own supplier?
Doing a win-win business is an art and playing right negotiation tactics to retaining the powerful supplier is always the first best option