Let’s for the sake of argument say that you only spent a month abroad before “being forced” to return. The only difference to a world traveller would be that you registered with the Swiss embassy (being a Swiss national). This document is what the Freizuegigkeitsstiftung requested from me. Not sure what documentation they requested from @BigVern.
So you get your lump sum payment during that month abroad, get taxed at source (Quellensteuer) based on the canton where your pension fund was held. And return to Switzerland, where you will be taxed based on your residency on December 31. You never took up tax residency in the country you moved to for a month.
Who will know what you have done?
- You will be asked on the Swiss tax form “where in this canton have you submitted your last tax?”. You will answer this truthfully with “Gemeinde XYZ” if you went back to the same canton. The tax authorities will immediately see that your wealth has grown by several 100k. They might ask for a rationale and then you would have to truthfully answer. A potential way around this would be if you move to another canton.
- As you have left a job for early retirement but have come back unexpectedly, you will probably apply for unemployment benefits. There you will be asked when and how much capital from the pension fund you withdrew. You will answer truthfully. Not sure what the consequence of this will be.
You might have a hard time to claim that you are something else than a world traveller. Maybe you have a long-term rental contract from the country you were forced to leave after only a month. This might help you as perhaps other arguments might help. Whatever you provide to authorities, they need to stick it into their mould, called “law” and “Kreisschreiben”. I concur with @Karl that we do nothing illegal when utilizing existing rules to the max.