To throw away an investment in space infra-structure the size of the ISS seems an incredible waste. Even if there is only a limited chance of ever using it again, the probability of this happening should be multiplied with the gigantic investment itself in order to reach an assesment of the potential value of the long term storage investment.
In other words, if there is 10% chance of salvaging 30% of the investment, it is still worth billions. Another aspect of the value of a determined salvage operation is the learning experience. By using the existing NEXT ion engines and the station's existing solar power array, NASA or whoever does it might learn something about cost effective industrial space operations, which hopefully will come in handy one day .
If The ISS were boosted to a height of 5000 km , it would be stable for a very long time . Without airpressure in the modules, many of the processes of degeneration of materials would efectively end , except maybe the ageing of gaskets and pressure seals.
While NASA has a 2015 plan for using the Vasimir ion engine for experimenting with ISS orbit boost, this has never been a real practical plan for boosting the ISS to a stable orbit, but rather a way to get more funding for a PET project...The total drag on ISS is about 0.9 N , a single NEXT engine can push 0.25 , 6 ion engines together with ''normal'' chemical boosts for 10 more years could go along way towards a stable orbit. The NEXT program has build atleast 4 prototype engines , probably sitting on a shelf somewhere .. WHY not use them ?