De Ruyter did not have an army, but the Republic was in an alliance with France at the time, so there's our needed army.
France in 1667 was preparing her army for the War of Devolution against Spain in the Spanish Netherlands. For the same reason the Republic needed a quick peace with England to later ally together with Sweden against France.
So basically, the Republic, while allied with France, launched the Raid on the Medway to achieve a quick peace with England so they could together form an alliance against France. (If you don't get it: 17th century history is complicated)
With that out of the way, if the cause of the War of Devolution is removed (the dowry for Maria Theresa is paid or Louis XIV simply sees the oppurtunity to take a big swip at perfidious Albion), the French army can be used to invade England: the ships of the line are burned/out of supplies and the flagship captured, so De Ruyter controls the seas around England.
The problem is of course that it certainly is not in the Republic's best interest to have France control England, so they will not cooperate with a French expedition. That's the whole reason why William III later launched his own invasion of England in 1688 when James II was acting as Louis XIV's poodle.
So politically, it's highly doubtful, but with the Royal Navy out of the way, there's no practical reason an invasion could not happen. As events in 1688 showed, the Republic was capable of having a good army in addition to its fleet, but De Witt would never allow that, as that would only strengthen the Orangist Party in the Republic (during the French invasion in 1672 it immediately cost him his life, so he was certainly right about that).