"Yes, he could, but there is security and hero students around." Yeah but UA's security system is shit as seen in the USJ arc. And UA being attacked while Deku is away would be a perfect narrative consequence for him constantly trying to act alone (esp if Inko gets badly hurt or even dies. Maybe AM too bc there's still Nighteye's prophecy). And if Hori's rly ending the "Academia" part of the story he might as well end it with a bang (as in destroy UA)
HOLY SHIT - a UA siege with all the parents there sounds like the perfect endgame!!! - it would give us high-stakes civilians to protect!!!. Also, it could actually take the pros completely out of the picture as ShigarAFO may lure them to a different location - leaving it ALL to the students and the teachers. (OMG, also this way Touya could literally face his entire family without them suddenly becoming all heroes).
As for Inko, I’m fairly certain that Deku probably asked Kacchan to protect her (whether in the letter or if they actually said good-bye). I just feel like he’d be the obvious person to ask. Or maybe he didn’t even have to, because he knows that Kacchan would do it. And because of this, I’m also 100% sure that Inko will be fine. I can’t imagine Bakugou would let anything happen to her in Deku’s absence.
But like, also, it’s one of my long-held fic-ideas that there is an attack where Bakugou goes to protect Inko and there is a really uncomfortable conversation about the past - because Inko doesn’t really know that they sort of made up. And Inko would say some harsh words about Bakugou being mean to Izuku, and she wouldn’t know that Bakugou almost died protecting him, and the angst potential is great.