my card is valid until sep 2028..if I am returning by the end of 2027 and staying in Canada for 730 days..is it sufficient to retain my pr status
I think
@YVR123 gave an excellent summary. You should note that this is mostly according to the law, rules and regs as of now, and a new government could change things - and/or even without changing much formally could attempt to make enforcement of the rules/regs much more 'strict' in ways that could be unpleasant. (I say 'attempt' because there are still judicial and quasi-judicial appeals processes which may limit how far they could go - but that can still be unpleasant).
If I may add a few minor things, mainly about what happens after you return 'for good' and having to stay the 730 days (assuming for the moment that you re-enter Canada without difficulty in 2027 - which is a big assumption).
1) When you return, and particularly after your PR card expires, it will become much more difficult and risky (for your PR status) to travel abroad much, and you may have to wait until you get that 730 days to apply to renew your card - meaning possible more than two years (as some of your days will expire). You may find - like many have before - that this is a SIGNIFICANT constraint on your life, career, lifestyle, etc.
2) As a specific example: it may not be possible to sponsor a spouse or partner if you are not compliant with the residency obligation - and with limited ability to travel, that can be devastating to a relationship.
3) Expect the unexpected: many other PRs have left with specific plans to return and then .... life intrudes. If returning and establishing yourself as a PR, anew, without travelling is hard and can be messy, doing so after things come up, your card expires, etc., etc., is more so.
Frequent causes / things that keep PRs abroad for longer than planned are/have been: health issues; health issues of/caring for parents; job opportunities/businesses; spouses/children; pandemics; etc., etc. Some of these may be 'good reasons' that get you some leniency, some may not. Even when there is leniency, it doesn't resolve all problems or inconveniences.
So overall, technically your plan might 'work' but be impractical on lots of levels. It can only be up to you.