There was a period when we used to hear of friends or relatives having to visit UK or Australia, to 'renew' their PR status! Soon, UK amended their law on this, and any UKPR leaving the country must return within 6 months, and had to stay for a minimum of 2 years, otherwise, they would lose their PR status. Of course, since then, the relevant law would have been amended many times and I am not sure about current requirements.
For those already in employment or business, it is unlikely they could meet those conditions. Even then, we had concluded that the most important seems to be money: if anyone has plenty of it, almost all countries would welcome him or her.
There was a time when many Malaysians, including wealthy ones, who applied and maintained their PR status in Australia (to the extent of actually living there for 6 months or whatever period required) just so that their children could benefit from the free university education then.
A few days ago, at breakfast, my regular 'kaki' mentioned about his daughter's Singapore PR status and seem to think the PR status is permanent and up to her to go back and work at any time in the future. I told him that offhand I think it is not correct, because PR is logically meant for those working in Singapore and once you are out for a number of years, you cannot claim you are a permanent resident for a fact, can you?
Back home, I searched on Singapore's PR status and was not disappointed with the information (in support of my view), though my friend would be disappointed with his wrong perception and the fact that his daughter probably lost her PR status already.
A valid Re-Entry Permit (REP) is necessary whenever a Singapore Permanent Resident (SPR) wishes to travel out of Singapore. It will enable the Permanent Resident to retain his/her SPR status while away from Singapore.
A SPR who remains outside Singapore without a valid REP will lose his/her SPR status.'