You cant decay all the way to silver,
Biggest difference you can see would be someone at diamond at the lowest of lows,
But yes, as the guy above said, the matchmaker will probably try to boost you to your original MMR, so that your mmr matches your SR,
This is in case of decay and not actual losses tho
But basing ourselves in what Jeff Kaplan said: The “smurfing” system will probably boost you quicker too,