Depending upon site, soil and tree health specific conditions, trees can co exist with fungal associates for a long time. Maintaining tree health and facilitating as full a canopy as possible to keep sapwood functioning at peak performance can be important. At the ISA International Conference I just attended, the work of Lynne Boddy and A.D.M Rayner was a frequent topic of discussion. I'm attaching a summary of their research paper here, along with a link to the article itself.
"It is argued that the development of decay in living hardwoods can best be explained in terms of the unsuitability of functional sapwood for mycelial establishment owing to its high moisture content and lack of easily assimilable nutrients other than within living cells. Decay occurs when these limitations are removed by any mechanisms which prevent or interfere with the normal functioning of sapwood. Recent concepts of decay in living trees have implied an active host defence against infection. This view is discussed against the alternative that non-specific mechanisms which maintain sapwood function will, by their very nature, prevent establishment of -ycelium of decay and stain fungi. The significance of mixed microbial communities in the development of decay is discussed, particularly in relation to the supposed requirement for specific sequences to overcome host defences."
In other words, the more of the canopy leaves are removed, the less water is transpired by the sapwood. As sapwood looses its function and dries/dies, it becomes susceptible to colonization by wood consuming fungi.
A holistic approach is infinitely preferable to having someone with equipment/payroll needs to fund, come out to tell you that your tree is best removed, and the quicker the better. If you want to consider all the options, pay for a consulting arborist to visit your site and perform a thorough assessment of the tree, what type of fungi is on it, what parts, if any, of the structural parts of the tree are compromised, and what is the tree doing to mitigate the problem with reaction growth.
