Ok so I beat the game an I lost a battle an mi dive is gone... Wut should..

Just do rescue missions and then you can unlock new dungeons and other things.

HM Dive can be found at B10F of Solar Cave if you lost it, it require a key (can be found in this dungeon) and a water Pokemon

After you beat the game (credit roll), collect the HM in Solar Cave, this include Waterfall @B15F, Surf @B20F. A Spinda collapse in your house, he will give you Transparent Feature and grant you access to Fiery Field (Entei, can't be recruit the first time enter the dungeon). Beat this dungeon and Entei will grant you access to Lighting Field (Raikou, can't be recruit the first time enter the dungeon). Beat this dungeon and Raikou will grant you access to Northwind Field, here you will encounter Suicune (cant be recruit the first time enter the dungeon). Also beat this dungeon and you can go to Mt.Faraway to fight with Ho-oh (cant be recruit the first time enter the dungeon). In this dungeon you can find Friend Bow @30F which +10% to your recruit rate, you have to find a key from Solar Cave to open the door here. Befriend Ho-oh and it will grant you access to Western Cave where Mewtwo lives @B99F.
If you buy the Southern Island Friend Area, this will grant you access to Northern Range after a Pokemon fly across your base in the morning (Latios). Beat this and you can go to Pitfall Valley to rescue Latias. After that, two of them will join your team.
Beat the Stormy Sea, check the mail to be grant access to Buried Relic. Here you can recruit Mew @B36F-B98F.
Recruit all legendary birds (when you go to the dungeons contain these 3 birds, *suspend* any job mention these dungeons) will grant you access to Silver Trench after you talk to Alakazam in Pokemon Square then 3 birds in their Friend Area. Here you will encounter Lugia @B99F. Befriend him and you will be granted access to Meteor Cave where Deoxys lives.
Last one, Wish Cave, where you find Jirachi takes lots of step to unlock. After clearing Pitfall Valley, and if Blue Sky Meadow Friend Area is possessed, go to talk to Medicham and Ekans in front of Whiscash Pond. Do an optional mission (any rescue job you found), talk to them again. Do another mission, only Ekans will be left there, talk to Ekans, then look for Medicham's rescue request at Pelipper Contact House notice board. Do the mission and Medicham will give you Wish Stone, which Jirachi after seeing it will grant you a wish.
Beating the game allows you to evolve in the Luminous Cave which is in the Wishcash Pond north of Pokemon Square