1 company taking over another's 401k plan

I'm not sure if this is complicated or not, just that I have not run across this before.  Individual A has a solo 401k plan for himself.  No other employees of his business.  Now he is going to go work for a small employer as their employee.  This new employer does not have any retirement plan.

Would the new company be able to "take over" as the plan sponsor of the solo 401k plan, allowing their employees to become participants as well as allowing Individual A to stay in the plan?  I don't see why not, but, it just seems odd.  This is not a merger situation since the company has no plan to begin with.

Thanks

It can be done.  Whether it is advisable or not is another Q.  Does the new employer want a plan?  By the time you get done changing the sponsor and everything that goes with it, it's probably just as easy (or easier) to write a new plan and have the guy with the plan now terminate and roll the money in.  There is potential liability for the new employer to take on an existing plan and little or no reason to take that on.

The "solo 401(k)" document very likely doesn't allow an entity with employees to use it.  I would expect them to have to restate the document before they could adopt his plan.  I agree with Bird that it would make more sense for the company to start a new plan and let him roll his balance into the new plan. 

… and the other question is whether it is wise for him to terminate the existing plan. 

Yes, by going to work for the other employer, does that mean he will no longer be in business for himself and have self-employment income?

If he still have material SE income, it may make sense to maintain the solo plan, and he maintains control rather than having those assets in another employer's plan.

Ultimately, the question must be asked: "Why would you want to do that when there are easier, less problematic ways to get to the same end?"  I may be dense, but I can't see why this would be a good idea.  No disrespect intended.