http://deckbox.org/sets/420940

I'm going to lose a lot of my main cards when standard rotates, I was wondering if anybody had any suggestions on what would work in the future to replace the INN block and M13

Based on the list you posted, you're not THAT hard up once rotation hits.

Correct me if I'm missing something, but I see you losing the following cards:

Avacyn's Pilgrim, Arbor Elf, Strangleroot Geist, Silverblade Paladin, Sigarda, Vorapede, Faith's Shield, Farseek, Rancor, and Sunpetal Grove.

Yes, this is a large share of the deck that is rotating, but even without anything from Theros being spoiled yet, there are plenty of suitable replacements.

Avacyn's Pilgrim/Arbor Elf - Elvish Mystic fills in some here. It might not be a perfect swap, but it's a good start.

Strangleroot Geist - Kalonian Tusker is a good option here. Sure it doesn't have haste or undying, but a 3/3 for two green is almost always solid.

Silverblade Paladin - Nothing is going to grant double strike like this here, but Fiendslayer Paladin is a pretty good start. 2/2, first strike, lifelink, and just short of pro-red and black... yeah... that should do well. If you're in need of removal, Banisher Priest could work here too - not as aggro, but it gives you a 2/2 and provides an option to maintain the pressure on your opponent.

Sigarda... well... nothing is going to be as effective here or as resilient to everything. That aside, Archangel of Thune is an absolute house and it works well with the board presence you're building. If you're hard up for something with hexproof, Witchstalker strikes me as a good option.

Vorapede - again, no direct replacement, but there are options. I would suggest lowering your curve here.... given the aggro-ish nature of the deck, you might want things that are a bit cheaper. Deadbridge Goliath perhaps?

Faith's Shield - this swaps almost seamlessly with Brave the Elements.

Farseek - we can hope we get something similar in Theros. Perhaps the one-drop land search spell in M14 in a total pinch.

Rancor - it will be missed... but two things are working for you here. First, Theros is said to be an enchantment heavy block - so it's possible we will see our little friend once again (or something comparable). Second, I would say to just up your count of Unflinching Courages.

Lastly, Sunpetal Grove - a few Selesnya Guildgates can work here. They're not ideal, but they're an option.

Obviously rotation will need you to rethink the deck a bit and work on things, but there are options.

He could splash red, replace the groves with sacred foundry/stomping grounds and add zhur-taa Druids to help with green mana fixing.