This is quite a question. Video tapes do not last forever and can be affected by mould and damp. Some makes are particularily affected by sticky tape shed where the physical structure of the tape disintigrates. Then there is dust and magnetic drop-out. Hard drive and solid state media can also become unplayable.
We make digital tape back-up copies in addition to DVD and Blu-ray archiving. Time will tell whether this is good enough or not. Another option that some of our clients like, such as the British Film Institute, is to back-up on to LTO tape, which has been designed for the job. We have invested in a plug and play USB3 LTO 6 drive which is available for hire. In truth, it is a bit of a hassle to set up but we can show you how to use it.
What do you do for back up? Please let us know.