Crab Apple Tree

I am hoping you can give me some advice about my crab apple tree.  I live in the Bayview and Steeles area of Toronto.  This tree was here when we moved in about 32 years ago.  The house is about 50 to 60 years old and I suspect the tree has been here from the start.  It is very large, in fact an arborist we had pruning it several years ago said it was the largest he had ever seen.
For the past few years it has been dropping leaves all summer long.  This year there were barely 20 % of the branches in blossom. I have been told the life expectancy of the tree is about 40 to 45 years.  Is this correct?  If so, do you think I should take the tree down now?  If not, is it worth investing the time and money to prune it?  I’ve bee quoted $650 to cut it down and $1200 to prune it.

Crabapple trees have a lifespan of 30 to 70 years, depending on individual climate, care and disease conditions.  Trees which are grafted onto standard apple rootstock will give abundant fruit for 30 years or more.  The sparse foliage on the tree and limited flowering is an indication that this tree is in decline.

Severe leaf loss over the past 2 seasons may be due to a fungal disease.  Apple Scab is very common after a wet humid spring, like we have just experienced.  It begins with olive green spots that turn black, and mid-summer leaves turn yellow and drop off.  The fungus overwinters in infected leaves, dead bark or fruit on the ground.  The spores from the fungus then start developing in late winter or early spring, and are released into the air by rain, wind or insects.  It then germinates on the new leaves when their surface is wet/humid and begins creating the spots.  Heavy infections cause the leaves to turn yellow and drop off at this time of year.

It may be time to take down this tree and redesign the area.