You are right that you are certainly in the Mahadasha of Mars and Antardasha of Mercury which is the lord of 2nd and 7th house, which are the Marka stana. Having said that a Marka Dasha does not mean that the native will die, simply by the name it has of Maraka. It means that the native will face health related issues can be there. It is indeed a difficult period , especially for death the badhaka planet also has to checked. I do not feel that you should be worried about Maraka dasha unnecessary. Doing the remedies of Mars and Mercury will certainly bring you gains, more so because Mercury is the lord of 2nd and 5th house and debilitated in the birth chart.