If you spend over 6 months outside of the US on any given trip, you break continuous residence. This means, you can only naturalize 5 years after returning from a long trip (or 3 years based on marriage to a US citizen).
If you spend over a year outside of the US, then you risk losing LPR status altogether.
I-131 sounds like a good idea unless you're returning shortly for good, which you aren't based on what you described.