From a UK tax perspective you can only contribute to an ISA while tax resident in the UK, but you get the whole annual allowance for a partial year of tax residency. You can keep the ISA while outside of the UK and enjoy tax protection from UK tax. The issue is that not every other country will recognise the ISA as tax-free, and it can be difficult to extract the tax records you need to declare the growth or income. Also, some providers won't allow you to keep the ISA open if you change the address to outside the UK.
Getting INC funds rather than ACC funds will make record keeping easier.
