After how much percentage loss in the total 'Futures' margin (Suppose in Nifty Futures), would I have to recapitalize it again?

It depends on your broker. But ideally with any broker one should maintain at-least span margin to carry position for the next day. During the day the position may be squared off above from some pre fixed percentage loss which is fixed by broker and it varies with every broker.

With Zerodha it can be at any level above 50% for intraday product type (mis) and above 70% for Nrml product type.

Markets are so volatile sometimes it may not give you enough time to fund your account so it is always better to equip your account with some free cash and use leverage manageably as it is a double edged sword.