Understand that respondents will be asked to fill name, password, reconfirmed password and CAPTCHA, etc. in order to resume later. Can we not ask the respondents to do that, and upon they click on "Resume Later", just show "Save Now" and "Return to survey". And upon they click back on the same survey link (with the same device), they can be redirected to where they left off? Is this feasible? Thanks very much!

If you use tokens you can do what you want, there is an option where they continue where they left off.

If you don't use tokens, there is no way for Limesurvey to know who started which survey, if you don't make them "register" first.