No, you have not bricked your ESP8266 by turning on GPIO7's pullup. All that will do is provide a weak pullup on the MISO line of the flash chip, which itself will have no effect - the flash chip's SPI Data Out pin will be able to easily override that weak pullup.
You can remove the flash chip and replace it with a completely blank brand new flash chip with nothing on it and still upload new code. There is nothing in the flash chip that the ESP8266 relies on to operate.
The boot sequence of the ESP8266 is as follows:
- Start executing the bootloader from the built-in ROM
- Read the GPIO pins to determine code execution source
- If flash is selected then initialize flash chip and read from address 0
- Code on flash examines partition table to find code entry point
- Jump to code entry point
- If UART is selected then initialize UART
- Wait for commands over the UART and respond accordingly
The startup code (boot stage 0) is in ROM. It's impossible to "brick" that. All that is in the flash is the code that tells the ESP8266 how to find the user's code, and that gets flashed to the chip every time you reprogram it.
You can think of it like BIOS boot on a PC. In the ROM is the BIOS that tells the CPU how to read from the hard drive. Then at the start of the hard drive is the code that tells the CPU how to load the operating system. The hard drive doesn't come with that code on it - you install that along with the operating system. But the motherboard has the BIOS built into ROM which tells it how to get going and read that boot sector.
However it is possible to destroy an ESP8266 by connecting the wrong things up to it in the wrong way. It is also possible to destroy some USB chips (the CH340G in particular) by wiring things up wrong.
So chances are that if you have bricked your ESP8266 it has nothing to do with your program and everything to do with what you have wired to it.