All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
First of all, we ask Allaah to reward you for being keen on observing the religious rulings in your dealings and we ask Him to forgive and have mercy on your wife and grant her Paradise.
As regards insurance, as you know, it is forbidden; it is only the cooperative insurance that is permissible; in this regard please refer to Fataawa 89816 and 81425.
Therefore, it is not permissible for a Muslim to participate in the insurance which you mentioned unless he is forced to do so or if there is a dire necessity for participating in it.
Saying that you might need treatment in the future is not certain, because it is also possible that you might not need it. And if this happens, you may be well off and able to get treatment without needing to borrow money with Riba (interest and/or usury) or participate in this insurance.
If we presume that you will be really in need, and are in necessity to borrow money with Riba and the like, then it becomes permissible for you to borrow with Riba in this case due to the necessity, but the necessity should be valued according to its proper value.
As regards your second question, if you were able to cover your wife and you did not do so, then you were undoubtedly sinful, and you should repent to Allaah in order to expiate for this sin.
For more benefit, please refer to Fatwa 86527.
Allaah Knows best.