The problem with the end game is that players who acquire others only have upside. In many cases, there's a a bit of reconfiguring of facilities but that's somewhat innocuous in the grand scheme and not detrimental to stock price. What's needed is a counterbalance to the upside, and a mechanic to keep the stock market competitive. 

This should come in the form of a property tax. Each time you acquire a company, you should be taxed an amount proportionate to the amount of claims you're taking on. The tax should tick each second with your other expenses. If you're cashless, you accumulate debt against the tax. 

This mechanic adds risk, uncertainty, and emphasizes timing of making an acquisition. You don't only need the cash on hand to buy out stock, but you need to be able to support the acquisition infra-structurally.