There are potentially 2 correct answers: the key is in the word “retail”.
Why? Because the merit-order curve refers to the wholesale prices.
If we take for granted a certain structure leading to a merit order curve (given) it means we are on a very short term horizon. As a matter of fact, the curve varies, in a country like Germany, every hour, given a certain structure of the generation infrastructure (that is the mix of power plant that exists, without considering new plants).
If we design our merit order curve, it might look something like this:
(Pardon the low quality,I drew this graph by hand on my tablet).
On the X axis we have the volumes offered, and on the Y axis we have the price at which those are offered. This is how a merit order curve is constructed, by aggregating the offers by various plants. The lowest marginal cost is going to be renewables (which have a very low variable cost, since they do not require inputs, practically: wind is free). Then we have nuclear (again, low variable costs) then coal, Gas, and finally peak power plant, which are the most expensive and only go online on days where there is unusually high demand. Yet peakers are vital for the security of the supply.
What happens when we introduce demand? We obtain the clearing price, on the WHOLESALE market.
It will look something like this.
The crossing between supply and demand will determine the settlement price. Only plants with a marginal cost equal or lower than the settlement price will go online. Plants that have a marginal cost will break even, whereas plants with a lower cost than the marginal will receive an extra remuneration which is called “inframarginal rent”.
So what happens if we increase the supply of renewables? Pretty obviously, the clearing price will go down, hence pushing out of the market more fossil fuel powered plants. However this is going to happen in the Wholesale market.
In the retail market, at least in the short term, most likely nothing happens. Some people might make more money: that’s the intermediary selling you electricity, however also that is not, in the long run a given.
Also, the price in the retail market is not only composed of the cost of electricity: there are also balancing fees, transmission costs, taxes and other items.
It also needs to be noted that “peak plants” also need to be remunerated, as they are a vital part, at least for now, of the energy infrastructure security. As long as cheap and scalable storage solution are not brought to market, we will have to keep those plants online.
And here is the issue with the whole picture: a generation technology, and hence a power plant, is only as attractive as it is able to cover all its costs: the variable, fixed, maintenance and cost of capital.
The conclusion? This is a complicated matter. We do not have a choice on whether reduce our reliance on fossil fuels. However always be wary of people who have simple solutions: there is no silver bullet and is going to be a long, and costly process.
Chainergy 
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