The Dutch actually intended to rather limit the collateral damage of the Raid at Medway. Cornelis de Witt (the de facto leader of the Dutch ) more intended to embarrass the English rather than crush them. To that end he order De Ruyter, the Dutch Admiral not to let his men plunder. But, assuming de Witt had a change of heart, or decided that he wanted to inflict some real pain on the English, they just might have been able to pull it off.
For starters the Dutch Fleet would have either had to skip burning the fleet at Chatham, or sail out of the Medway River and then sail down the Thames. Chatham is a bit far from London proper to land troops and march on London, plus the troops/marines would have had to cross the River Thames to get to Whitehall and Westminster. However, the fleet would still be blocked by the London Bridge, unless they planned on blasting it into the river (London Bridge...falling down

) So the marines would either have to disembark east of the city, further up the further up the River Thames, or 30 miles south of the City at Medway.
If it were were the goal of the Dutch to pillage London, they probably would have skipped attacking the English Fleet at Medway, brought along a lot more Marines. IMHO they did not have enough men with them to accomplish both.
Sailing down the Thames River would have been a separate challenge from sailing down the Medway, since there were fortifications such as Tilbury Fort. Judging from the performance of the English garrison at Forts Upnor and Sheerness, Tilbury might not been that great of an obstacle, but, seeing as the fort is the ONLY barrier to a foreign fleet sailing into London, I would think it would be adequately garrisoned and armed.
Assuming the Dutch Marines manage to make it to the city either by marching overland or forcing their way up the Thames, they would face a rather challenging target for pillage. Half the city had burnt to the ground about nine months earlier (the 1666 London), leaving behind a perfect terrain for defensive urban warfare for whatever English troops were around London to dig in. Those troops would at least consist of the 1st Foot Guards, and the Coldstream Guards, and they would probably assemble to oppose the invaders. Altogether that would be over a thousand elite line infantry to face 1000-1500 Dutch Marines who had already disembarked and fought that day at Fort Sheerness, and at Medway.
If the Dutch Marines pushed aside the King's elite Foot Guards, and sacked London, it would have seriously undermined the English monarchy. The Raid at Medway was a national embarrassment, the sack of the national capital would have discredited the recently restored Stuart monarchy. Charles II feared a revolt from the Raid, with a sacking he might have faced just that.
As far as the Treaty of Breda, I think at minimum the English would be giving up their conquest of the New Netherlands, and possibly repealing the Navigation Acts, which were a major cause of the war. This would be on top of surrendering Suriname to the Dutch.
Of course the English would no doubt look forward to the next Anglo-Dutch War with great anticipation, and likely contribute much more on the side of France during the Franco-Dutch War of 1672.