As you left the UK in 2016 and did not return to live in the UK within 2 years of the date you left, your ILR will have become invalid in 2018.
You have to be returning to LIVE in the UK within 2 years of first leaving (2016) in order to keep your ILR valid.
You may have been lucky the last time and still been stamped in on your ILR, but that is unlikely to happen again, as you should have been stamped in as a visitor to the UK, which would have cancelled your ILR right away.
So, really, regardless of whether you are able to fly to the UK before May or not and regardless of whether your ILR is valid or not, you are not eligible to enter using your ILR because you are only visiting and not moving back to the UK (and even if you were moving back, you still would not be eligible because it’s been more than 2 years since you moved away from the UK).