Lets see how much you can put in your portfolio. 

Developing drawings are more important than rendering. I would suggest represented the render, only necessary, in the way that can best describe your work, concept, etc. 

sorry to hear that. I can't image what I would do but I can suggest this:

besides drawing skills, schools are also looking for new means of communication to transmit architecture work. for example you can eloquently write about your projects and use a typographic language to enhance that experience but also show your architecture skills within the text or additional drawings. 

here is an example of typographic design just as a reference.

That sucks big time. My school burnt down in 2008 and some students and staff lost their entire thesis/models/research.

No clear advice as of what to do, just use as much as you can of the materials you still have and is worthy of being in your portfolio. Redoing some of it might also be an idea, it usually goes faster the second time, just like with software crashes. Or see it as a second chance to improve some of your projects :-(

agree, it sucks.  My car was stolen shortly before applications were due, lost everything.

Just redo everything. I'm currently in the process of completely redesigning every project from my undergraduate studies to ensure a better portfolio, so you're not alone.

Really? One could look at it that s/he is going above and beyond ('trying hard') by taking the initiative to spend their own time improving their undergraduate projects to show their best work to potential graduate programs. Updating those projects will make them better. I spent a couple months prior to grad applications updating a lot of work to reflect my better skillset, ended up being a great decision.

Lighten up a bit damnit! You've been particularly cranky the last couple weeks.

If you can learn a new skill that communicates the idea better after the fact and want that reflected in your portfolio that seems fine to me. If your angle is to show how you've grown and progressed from studio class to studio class then that's fine, but that's a different goal than what the OP describes.

+1 for redoing/enhancing portfolio

Especially for grad school admissions, the respective offices would want to gauge your creativity wrt presentation/unfettered brief/analysis etc. It's also important to demonstrate how you've managed to walk through the design process from conception to documentation, all of which requires the aid and guidance of a tutor.

Other alternatives would either be to get an internship (which won't do you much good to your growth); take a different workshop/masterclass (you should however already be familiar with technical programs by the end of your BArch); summer schools (which requires money).

Sorry to hear that. I went through the same. I redesined few academic projects, did few competitions and workshops. I applied to 3 schools and got offers from all of them. In London Met (open doors day) I heard that my portfolio has lack of hand drawnings which shows design process. It's really neccecary. Redoing 2-3 academic ungrad projects take some time, but it's not imposible. And you have a chance to improve it! Good luck!