I left the UK many years ago, and have deliberately cut many ties such as an available house to live in (ie not rented out), etc etc, but have always maintained UK bank accounts, a UK mobile phone no. for work, a UK address for post (which has helped enormously for visas when a police clearance certificate is required), etc. You maintain what you need but cut ties with the rest.
I've been non-resident in the UK for tax for many years. Three years ago we visited the UK and my wife (a tourist on an Aussie passport) developed a problem. She received free emergency treatment from the NHS, but we had to pay for necessary surgery afterwards. There's a fine line between emergency treatment and subsequent necessary treatment. We were covered by insurance so no worries.
My understanding from our dealings with the NHS from then, is that even if you have been away from the UK for years, you can go back and receive free NHS treatment so long as you can convince them that your intention is to stay and resettle in the UK from then on. I have no idea what that actually means, or how it's applied, in practice.