When film is produced, it is made in huge master rolls, thousands of feet long and many feet wide. It is then cut/sliced into 35mm strips and 120 strips and wider strips which will be later cut to the sheet film sizes. So, as long as someone is making film, and there is a market for it, 120 will be available because it isn't purpose-made like one might think, it can be cut from the master roll so it's no biggie to "make" it.
Even if a single master roll cannot be multi-purposed for different film sizes, master rolls would still be produced, and deciding to use one every now and then for 120 film strips would not be an insurmountable problem.