Look at the end of the series. Tony was either going to get whacked or get indicted, as his lawyer said was likely to happen. Silvio was still in the coma, and he might have not came out in time to become boss. If he didn't come out, there would have been a power struggle, possibly between Paulie and Patsy, or other capos. In this power struggle the Jersey Family would be heavily crippled with much of the leadership taken out and crews became thin.