When Jesus comes back and returns the world to perfection, do you think he will cause all evidences of the current worlds infrastructure, such as building, highways, etc. to disappear? No modern power grids, transportation systems, everything as it was when Adam was alive? Or do you think there will be evidences of the world’s previous situation? If the seas are dried, then it wont serve up images of the past that were covered by water? And without boats and planes how would people travel to celebrate the feasts, as will be required?
The Bible calls this time the restoration (regeneration, renewal) of all things (Matt. 19:28, Acts 3:21). Although two different Greek words are used in these references, they both mean to restore something to the original pristine state it was in before it was damaged. This applies specifically to the effects upon the creation caused by sin. This means the weather will always be good, the earth will cooperate in the production of food, man’s lifespan will increase, his work will be a joy, and never again will he work primarily for the benefit of others. Isaiah 65:17-25 gives a good description of this. As for the so-called modern conveniences, which have only been part of the creation for the last 100 years or so, we’ll have to wait and see.
The seas became a part of creation after the flood. Mountains were raised up and valleys lowered to accommodate all the water. Much of this water will be taken up to restore the canopy that surrounded Earth before the flood (Genesis 1:6-8). If this process is reversed and the valleys are raised up, perhaps reuniting the continents, then much of the evidence now covered by water will disappear. In any case I don’t think the Lord will leave gaping wounds in the Earth’s surface where the seas used to be, complete with the uncovered ruins of fallen civilizations, to mar the beauty of the restored creation.
And if the Lord requires all the people of Earth to attend the Feast of tabernacles as in Zechariah 14:16, then He’ll provide the means of conveyance.