First, the default GRUB 2 configuration for Ubuntu sends GRUB 2 to the Ubuntu partition for some critical configuration and support files. This makes GRUB 2 reliant on files on both the EFI System Partition (ESP) and the Ubuntu root (
/boot partition. Thus, deleting the Ubuntu partition almost certainly did not damage the EFI System Partition (ESP). Instead, you deprived GRUB 2 of its configuration and support files, leading to an inability to boot through GRUB 2. This problem is actually easily overcome by using the computer's built-in boot manager -- typically accessed by pressing Esc, Enter, or a function key when you power on the system. (Unfortunately, there's no standardization in user interfaces, so I can't be more specific.) If you'd known this, you could probably have saved yourself a lot of hassle.
Second, installing Ubuntu without a boot loader is pretty pointless, since a boot loader is required to boot an OS. That said, the boot loader need not be GRUB 2. This question and answers briefly describe several alternatives. My Web page on the subject goes into a lot more detail. If you want to use something other than GRUB 2, you can boot the installer using the "try before installing" option, launch a Terminal, and type:
This command launches the installer and tells it to not install GRUB. When the installation finishes, you'll have to install the boot loader of your choice in some way. Options include:
- Install it from Windows
- Install it from the Ubuntu live disk
- Use an emergency boot manager like rEFInd on USB drive to boot Ubuntu, then install from there
If you want a boot process that's safe from problems caused by deleting Ubuntu, you'll need to either use something other than GRUB 2 or create a heavily-customized GRUB 2 configuration, as described here. (Note that, although that page includes a comment that it's outdated, the newer page does not describe how to create a custom GRUB setup.)