Why are the seventh & 8th centuries missing from Indian history?

 Because that period is dominated by Southern, Western and Eastern Indian dynasties .

Harshwardhana of kannauj the king who was never defeated in a war out of 599 Battles he was involved in ,was Defeated by Immadi Pulekeshi a kannadiga king of Chalukyas . Kannada inscription of 650ad states Harsha lost his Harsha (smile) after being defeated by Pulekeshi2.

The Naramada river became the Border between these 2 Powerful Kingdom between 6th to 8th century .

Harshawardhana was later given the title Utterapateshwara (Ruler of the North) , Pulekeshi was given the Title Dakshinapateshwara(Ruler of the South) .

Later Rashtrakutas , Gujratha pratiharas and Palas , A kannadiga, Gujerathi/sindhi and Bengali dynasty were in tripathit struggle for the domination of Central India between 8th century to 10th century .

From 10th to 13th century chalukyas of Karnataka made a comeback and were at logger heads against Eastern Gangas of Odissah and Cholas of Tamil Nadu

So because of Weak politics of Karnataka , Gujerath , MP, odissah and Bengal we are not able to bring this part of History to Indian History Books .

Which former batsmen's replacement is the Indian cricket team missing even now?

 In Kohli we have a proxy for Sachin. In Ashwin you can find an intelligent Harbhajan. In Pujara and Rahane combined you will see shadows of Dravid but if we talk in particularly about a batsmen whose replacement has yet not been found, my answer would be Virender Sehwag.

Now, this is again debatable with the super form of Rohit Sharma in ODIs, T20s and now in tests but even Rohit Sharma is not the batsman who will hit you with ball 1. Indeed he is a batting giant and score daddy hundreds in ODIs but he take his time initially and that strategy backfires sometimes because the Power Play is wasted. On the brighter side this happens not so often :)

Having said this, Virender Sehwag scored 8124 runs at an average of 50.14 and a strike-rate of 83.06. That strike-rate meant that when he was at the wicket, the match moved forward.

It is incredible that Sehwag achieved so much in his career with minimum footwork but one thing that goes his way was top class hand-eye coordination. If he is in the zone the match may finish on Day 1. Even if he departs early he had capabilities to hijack bare minimum opening session by producing fiery 30s and 40s and in the process a stormy opening for Team India.

Shikhar Dhawan was a pretty aggressive batsman but his strike-rate is 66.94. Still pretty high by Test standards. But Sehwag’s strike-rate was 83.06. When the right-hander from Najafgarh got a start, India would take charge of the game.

Murali Vijay used to take plenty of time. A good opener but remotely closer to Sehwag.

KL Rahul is a player with great technique. He is aggressive too. KL’s inconsistent form has been his biggest enemy and led to his downfall.

Prithvi Shaw and Mayank Agarwal are just making baby steps as openers and comparison with Sehwag will be irrelevant

Now with Rohit Sharma 2.0 hopes are again phoenix-ed but it is still a long way to call him Sehwag’s replacement. Screenshots below will help us to understand why?

When Sehwag was in the crease,this type of scorecard wasn't shocking in ODI's.

VB Series. Venue: Australia. Result: first ball Six

The pitch is dangerous, the spinner is a mystery: NOT FOR ME

Team score 141–0, Meanwhile Sehwag

This is before T20 era

We need another 300. Sehwag: Noted