I was playing a quick game, and my opponent played Shidako, Broodmistress and attacked with several creatures, I declared my blockers, and my opponent proceeded to pay the forests and sacrifice all of the creature I blocked to buff the one that got through, my question is, now that all of the creatures I blocked are no longer attacking, am I able to redeclare blockers, due to the change of creature prescence?
No. The step for declaring blockers only happens once, followed by the ability to play abilities and effects, which can result in any number of situations including attackers or blockers no longer doing so, being destroyed, buffed, or whatever. Regardless of the circumstance that results, blockers cannot be changed and the players must deal with the consequences of the units continuing with their combat orders to the best of their ability.
No; once blockers have been declared, play moves to the Combat Damage step. Because your opponent's action happened after the Declare Blockers step you can't re-declare your blockers. But the good news is you don't have to:
If blockers have been removed due to exile, card return or sacrifice, the blocked creatures still count as blocked and resolve their damage against the non-existant blocker(s)!
This is actually very helpful, as you can declare a blocker and then sacrificie it for it's sacrifice ability or pull it back to your hand to keep it safe.
From the comp rules:
509.1h An attacking creature with one or more creatures declared as blockers for it becomes a blocked creature; one with no creatures declared as blockers for it becomes an unblocked creature. This remains unchanged until the creature is removed from combat, an effect says that it becomes blocked or unblocked, or the combat phase ends, whichever comes first. A creature remains blocked even if all the creatures blocking it are removed from combat.