@CounterStrike- Those seasons weren’t as boring as seeing posts by people like you failing to accept that the German fellow won 5 titles in a row.
With regards to the main topic- I see Honda returning first, perhaps when the next set of engine regulations are brought in. They usually can’t stay away from F1 for long, so they may well rejoin in the future. I have a gut feeling that Peugeot would be the last to return.