I assume from your phrasing you mean to say that "some industrialists will prefer human labour over cheaper machines". (But you could instead have meant to say that "in society, there will always be a role for human labour").

I think this proposition is false (in the long run) due to the the profit-maximization logic of capitalism. Even if some industrialists prefer human labour, in the long run they'd eventually be out-competed by those that didn't. But yes, machines cost a lot upfront which could delay the switchover (possibly even beyond the sunset of the industry!).

I think the "Rate of profit falls" theory doesn't matter. Assume it's true: machines lower the rate of profit. But, capitalists can't (as a group) decide not to use machines. Without control of private assets (e.g. capital) the capitalists cease to be, and become a purely rentier class again. It would no longer be capitalism but feudalism. I don't believe capitalists have the power (or desire) to cause such a transition.