Such forecasts aren't my forte: I'd imagine that - with almost bottomless (governmental and EU) encouragement, support and resources - research (and testing) of alternative energy sources will be massively accelerated, and - as we saw with vaccines for Covid - may well happen far faster than some forecasts had envisage.
I would further imagine that such research may well take place on several simultaneous fronts, (wind, solar, tidal, etc) and some may yield unexpected dividends.
Five years?
To be honest, I'd be surprised if there wasn't an enormous reduction within a year, or 18 months, or certainly, two years.
The thing is, by (so openly) threatening Europe's energy supply, the Russians have absolutely guaranteed that Europe will do almost anything to ensure that they are not in thrall to it, and not reliant on it; nothing could have achieved this more rapidly than such overt threats, which - in the long term - will hurt Russia enormously.