Hmmm I would do it all mate especially the water pump for me that is more likely to go before the tensioners but I would have them done at the same time. Once the bearings lose their cushion which is the grease things go downhill pretty fast. and you will find yourself back at the garage paying for it all to be done again, with the extra work :( Best way to look at it is will they last until another cambelt change is due. The extra work shouldn't take you much over an extra £100 for the piece of mind and risk it's worth having done I know it's all money but worth it in my honest opinion :)
And a good picture of one when it fails I think if not replaced in time