I recommend a complete refresh of your installation, because Steam should not crash if you lose connection:
- Completely exit the Steam client.
- Open the run dialogue by pressing windows key + r (you can also navigate here from the start menu by typing run).
- Type steam://flushconfig then press enter. (If asked to allow this website to open a program, please click Allow or OK).
- Restart your computer.
- Now, launch Steam directly from the installation folder, not from a pre-existing shortcut (~C:\program files (x86)\Steam).
- The Steam application will either appear as Steam or Steam.exe depending on whether your settings show file extensions.
If this does not help, there is more wrong than just your wifi adapter. I have wireless too and if mine is disconnecting for whatever reason, Steam just stops downloading.
As a further workaround, you can use this batch script:
REM Do not display commands
REM Loop Marker
echo Looking for Steam
tasklist /FI "IMAGENAME eq steam.exe" 2>NUL | find /I /N "steam.exe">NUL
if "%ERRORLEVEL%"=="0" (
echo Steam is running
) else (
echo Restarting Steam
ping 192.0.2.2 -n 1 -w 5000 > nul
Put it on your desktop in a textfile and save it as "check_steam.cmd" and run it before you leave your computer. Make sure you have fileendings on, so you really remove the .txt ending and save it as .cmd. The icon should change to a window with some cogs.
It simply checks if Steam is running and if not, it relaunches it. You can cancel the script at any time by pressing Ctrl-C in the black window that it opens and answering the question with Y.
For further problems with your computer that do not involve any gaming related software, I recommend asking on superuser, which is a site of Stack Exchange.