There are very low effort ways like target date funds. Of course, that means you have to pro-actively take money out of your paycheck and deposit it.
A bankruptcy does not mean the pension funding is gone. In the case of Sears it transferred to the PBGC with the federal government. In my case, the pension administration is handled (well outsourced) by the current owner of my long ago employer.
I've never heard of such a thing. For me, it's always been a choice of funds (and maybe company stock) held at a brokerage that allows me to reallocate investments as I wish.
I have to believe that if a company is "managing" 401k investments, it's just an abstraction on top of some agreed-to investment strategy at the brokerage.
Depends on what you mean by "manage". The money is explicitly yours, the company can never touch it. However; you are locked into the company agreement with the custodian (e.g. Vanguard and their list of investment funds).
Not locked. You can roll it over into a IRA/ roth IRA and manage yourself. You won't pay early withdrawal taxes as long as you roll over within 60 days.
I think after Sears and the rest, people prefer money now vs money later. But if I knew the money was good, I'd rather not manage it myself.