Yes, definitely try to get the chain removed or adjusted. The tree might possibly be able to grow around the chain, but, the chances of it dying, instead, are much greater in my opinion, if nothing is done. Even if the tree were about to grow around the tree, the tree would be weakened at that point and still much more likely to fail at that point. Also, I agree with others above that no further treatment is needed. I know, first hand, about the decision of how/when/if to approach a neighbor about such a situation. If it's a neighbor I see frequently, I would usually just mention it casually and hope they take the clue. In your case, and if the tree has the possibility to fall on your property/house if it falls, I'd probably feel more empowered to suggest that something be done. Preventing your house from being squashed definitely is not overreaction.

its dead .. cut to ground.. ignore rest ... unless you need that precise spot for something else shrooms are one of natures decomposers ..... it is doing its job, decomposing a dead tree ... do not be surprised.. if you dont see them popping out of the ground for the next decade.. as they decompose the rather massive dead root system ... frankly.. i consider them.. a free show of ma nature ... you cant really go planting a garden of them.. so enjoy them.. while they are around ken

Rhizo...Boy do we owe each other a letter!! MY mother has been asking about you for days and if you still had slippy's? I've missed you.. That's good for Mrshigsy..lol I was beginning to woner..lol So happy to see you Rhizo)

As stated above if the current owner hates it, they will do as they want, but As far as removing things that have grown into the tree's one branch or 2. The tree has dealt with it years ago. Trees have encapsulated bicycles, ropes and who knows what else, the main trunk is most important and they could likely deal with that stuff. If the owner got rid of the trees canopy above and saved the fern, the fern would die without that canopy ( I strongly believe) that the ferns ( because most ferns need shade) would die. If I were the owner I would maybe water deeply infrequently, but, you don't want to change things too drastically. I would've never thought a Southern Mag w/ Staghorn fern would be in a dry area in Cali. That's rare. I saw one large Staghorn fern in my life in Florida. It was in a large container on a tree trunk. It had some sun, but, most ferns, I have about 6-8 and they all want shade, so I would not get rid of that canopy and plan on keeping that Stag, fern. Plus that tree is very nice and rare, but, it's the owners choice overall. There have been pics years ago posted of bikes and other weird things leant against trees and never moved, and the trees just grew around these things. The trees will never be harmed by these objects unless someone tries to take them out. Maybe a rope for a swing only partially grown into the tree then used by a heavy adult would be worrisome. But, well, lets hope that wont happen.