Great question! I learn something new throughout each day here. :)

No worries if you,do not change your permalink and update your sitemap

Personally I like the permalink and the title to have some sort of relationship. I think that it looks better from the viewer's point of view. If I end up changing the permalink I add a redirect as you suggested.

So if I am say reviewing Product A, and my keyword is "Product A Review", I usually use a permalink of "Product-A", the title may be "Product A Review - Is It Any Good?", then if I update it I may change the title to "Product A Review - Is It Any Good? (Updated)".

I also usually change the SEO title to the same wording as the post title (if space allows) and may change the SEO description if I think it requires a change.

Make sure that the permalink does not have a year reference in it, so it does not become outdated (even if the content is updated, if a person sees a year two or three years back, they may not even look at your post).

Loads of opinions here in WA. The hard bit is determining which opinions work best for you.

A title change won't require a 301 redirect or cause a 404 error. Only if you change the permalink (don't change it) will that happen, so change the title with no worries.