wondering what age willows can expect to live to. We have an older one - around 40 yo, I'd guess and many dead branches. Is it worth getting it pruned at this age or should we just go on and cut it down and plant new ones. It is on the bank of a small stream, so that should be in its favor.
I wouldn't cut it down unlesss it was hazardous. Hazardous meaning is there a target (house, building, people) it could fall on? Some willows are considered weak wooded and short lived, but that doesn't mean yours won't live for a while longer. could you post a picture of it so we could see if it needs pruning or removed? if it is questionable, have a certified arborist or your county extension agent to evaluate it first. if there is ample room, you could go ahead and start to plant new ones that will already be planted when it does need to be cut down.
I have seen willows about a 100 years old still doing well. they do tend to get deadwood inside, dont be afraid to have this pruned out properly. I agree, if there is no target, it is no hazard. Get a qualified arborist to check it out and give you an estsimate based on ANSI pruning guidelines for a crown cleaning (referred to as 'cleaning' now but I feel adding the word crown is still more descriptive). If the county extension agent is a free service that is knowledgeable, have them out too! we dont have them in Canada so I am unfamiliar with what they can offer.
We have two huge willows, could be about that age. We got them pruned "properly" last year. It took all day with a guy in each tree; cost nearly $2000. Now mind you they were working around wires and in tight urban quarters; could be cheaper and faster if out in the open. They did a great job, and we are really happy with the outcome, but removing the trees would have been cheaper, apparently, though not much. But of course the pruning will be a repeated cost, and the cost of removal will eventually be incurred in addition. I'd call a stream a target, as the water course might be damaged by a tree falling on it.
Wildlife agents recommend putting logs in streams to enhance habitat. Damming one so it floods adjacent property, where such an occurrence would create problems like structural damage would not be desirable, of course. A big goldtwig willow I spotted near Stanwood, WA was a champion for a short time, blowing over not long after. Wasn't obviously decrepit. Some trees go quick, especially when taken out by adverse weather or other mishap rather than aging and decline.
Your willow can withstand wind better if it's thinned. The dead limbs allow the wind to tug on the tree much harder in rainy weather, than if it was pruned right. So if you have it pruned, the winds will pass through it easier.