Welcome to the forum and thanks for your question. I've very sorry to hear of your wife's tragic illness and death. Please accept my heartfel condolences and best wishes. I hope the following comments can help you adjust to it all.
Despite how difficult as the situation has been, you should not feel any guilt or personal responsibility for the HPV infection that led to her cancer; nor should you assume guilt or responsibility on your wife's part. It is almost never possible to know when and where any particular HPV infection was acquired. If she ever had sex with anyone other than you, it is equally likely (perhaps more likely) that another partner was the source of her infection. Even if she never had sex with anyone else, some HPV infection appear in virgins -- it isn't common, but it happens.
Whenever the responsible strain of HPV was acquired, and from whom, development of cancer is just bad luck. Almost all sexually active people acquire genital HPV at one time or another; probably most of us are infected more than once. The large majority of genital HPV infections are cleared up by the immune system. Even with the highest risk types, over 99% of infections do not lead to cancer; and when that happens, the large majority are easily curred by LEEP and related procedures. Your wife was very unlucky -- but that's all it was, bad luck. Her outcome was a rare one and neither of you has any responsibility for it.
My guess is you have asked your specific questions of your wife's gynecologist, cancer specialist, your own doctor, or other health professionals. If so, I'll bet their replies were similar to mine:
1) Invasive cancer probably sometimes can result from "low risk" HPV types -- but it's probably more likely she had a high risk strain that was missed by testing. But that didn't make any difference in her tragic outcome. Treatment for cervical cancer depends only on the cell changes seen on pap smear and biopsy, not on whether HPV is detected or what type is found. That her DNA test did not detect a high risk strain made no difference in her treatment or the development of invasive and metastatic cancer.
2,4) Within each high risk type (e.g., HPV-16, 18, etc), there are no known differences in cancer potential. And it is very unlikely you are currently carrying the HPV strain that caused your wife's cancer; if you ever had it, probably your immune system eradicated it long ago. Even if you still have it and were to transmit it to a future sex partner, the chance she would develop cancer is no higher just because it happened to your wife.
3) HPV testing is not recommended for the male partners of women with HPV, with or without dysplasia or cancer. In this situation, I can understand your desire to know more. But there are no standard methods to test asymptomatic men for HPV. Even if you could find a doctor or lab to test you, a negative result would not prove you don't have it; and nothing can be done for positive results without symptoms.
I hope this information at least starts to put your mind at ease. Best wishes to you and your family.
HHH, MD
I thought of one additional bit of advice. In the event of a future sexual relationship that may become mutually committed, before you stop using condoms you probably should have a discussion with your about your wife's illnes. From a strict infection risk perspective, it may not be necessary, for the reasons discussed above. But still, many women would want to know this information. Your partner could consider immunizaation with Gardasil, the HPV vaccine that would protect her from at least some of the HPV strains that could have been responsible for your wife's cancer.